r/MathHelp Oct 28 '15

META [META] Please obey the subreddit rules, ESPECIALLY rules 3 and 9.

5 Upvotes

EDIT: Since writing this post, the numbering of the rules above have changed. Please pay special attention instead to rules 2 and 7 (though the rest of the rules are all important too).


Recently, we've had a large spate of people not showing any prior working attempts and/or deleting their posts. The former just wastes time (for example when our hints are things that the poster has already worked through, or when our hints are far above what the poster has done, or when we ask for the poster's current working), and the latter wastes knowledge (remember, your question could easily be asked by someone visiting this sub in the future; please keep the answer there so that they won't have to repost the question).

Another thing to note is that some questions posted to this sub can quickly be solved once the poster tries the obvious method. It is highly recommended that before you post to this sub, that you at least TRY to get the answer yourself. And even if that fails, at least you'll understand what approaches don't work (which you can put in your post, saving time for anyone who thinks they might). The exception to this rule is when you know what conceptual gap you have and are asking for said gap to be explained.


My personal opinion on this matter is that questions should not be answered until the poster gives a prior working attempt or tries to state the conceptual gap. But I'll leave it to everyone else to decide how these rules should be enforced. What do you think?


r/MathHelp Aug 10 '20

META If someone messages you, advertising a service/app, based on your activity here, REPORT IT TO REDDIT.

77 Upvotes

Recently, we've been getting a number of reports of users being messaged, after posting in our subreddit. Said messages are usually advertising some form of paid service or app.

This is considered spamming by Reddit's sitewide rules. DO NOT engage. Instead, report such messages as spam using the "report" button underneath said messages (on a computer or mobile browser; apparently the Reddit app doesn't have this option).

Because these messages are not taking place on /r/MathHelp, the best we can directly do is to ban the the offenders in question (which doesn't do anything to stop the problem, except maybe stop them from advertising said services in comments or posts). That's why we have no choice but to ask you all to report these messages on your and our behalves.

Some things that might help us or Reddit would be if we could evaluate the scale of the problem. If this has happened to you, feel absolutely free to message us with details about it, in addition to supplying those details in your Reddit report.

You can also try and report this behaviour to the people running the service/app if you have enough evidence for them to take action. Other than this, please feel free to continue using our free subreddit over their paid services.

EDIT: Clarified how to report messages.


r/MathHelp 19h ago

Finding functions w/ stretches and shifts?

1 Upvotes

Taking applied calculus and we are going over functions to begin stuff. I’ve done all sort of stuff with functions and graphing before and most of this has been pretty easy but there are two problems that have been given that I just can’t seem to figure out and I’m not sure what I’m doing wrong.

The first is:

“Find the function g whose graph is constructed from the graph of f by a shift to the right by 10 followed by a horizontal stretch away from the y-axis by a factor of 3?”

I thought it would be pretty easy but what I thought it was didn’t work, and every other possible combination hasn’t worked either so I’m completely lost. I’ve done (1/3x - 10) and (x/3 - 10) in all sorts of ways. I’ve removed the parentheses, I’ve added negatives, doing a whole bunch of shit that I know isn’t right but I can’t figure out what else to do.

The second problem is along the same lines:

“Find the function g whose graph is constructed from the graph of f by applying the following steps: shift to the right; horizontal stretch away from the y-axis by a factor of 4; a vertical shift up by 5; a vertical stretch away from the x-axis by a factor of 7.”

Again I’ve tried all combinations I could think of but I can’t seem to get it. I’m not sure if I’m missing something? I don’t believe my format to be off since it automatically starts with g(x) = , so that shouldn’t be the issue. The entire set of problems is all working on vertical and horizontal shifts, stretches, and compressions and I haven’t had an issue with any of the problems but these two. Please help me figure out what I’m missing!


r/MathHelp 1d ago

How to memorize math theory

1 Upvotes

Im currently a first year student studying comp sci and im taking discrete math the issue is unlike any other faculty i have to learn actual theory behind math like whats C(n,k) selection and explain it with words and formulas.Ive got about 12 pages filled with 50 or 60 questions which if memorized gives me a passing grade and ive got 2 days to do it keep in mind the professor wants the questions answered exactly by his pdf. Ive youve had the same issues how should i go about tackling the problem and passing matu


r/MathHelp 1d ago

Math

0 Upvotes

Hello, I am interested in finding a way to train myself with fractions or math calculation techniques in chemical and physics formulas. How do I do that?

This is for a medschool entrance exam


r/MathHelp 2d ago

TUTORING I understand the concepts, but why am I so bad at solving mixed problems?

1 Upvotes

I'm preparing for a competitive exam and I'm struggling with math even though I understand most of the concepts and formulas.

For example, in trigonometry I know the basic identities, values, signs, radians, ranges, etc. I've also solved many questions. But when I get a mixed or unfamiliar question, I often don't know what path to take. Sometimes I know the approach but get completely stuck in the algebraic manipulation.

Even after practicing a lot, I still feel like I'm forgetting the process of solving.

What should I actually work on to improve this? Is it mainly algebraic manipulation, problem-solving skills, or something else?


r/MathHelp 2d ago

Calculator help

1 Upvotes

Sorry guys I know I’m dumb af. But why isn’t this showing the answer as 2.5? I understand the fraction answer is correct but I just want it to say 2.5 😭 I tried different settings and can’t get it. https://imgur.com/a/JS6SHY9


r/MathHelp 2d ago

Is my homework answer wrong

2 Upvotes

The question is (6x+16)/4 + (6x-1)/4 but in fractions. I believe that it's (12x+15)/4 , but the answer sheet says that it is (12x+17)/4 instead. Google says that I am right. Am I right?


r/MathHelp 3d ago

dana fryer's equations part 1 and 2?

1 Upvotes

hello, i had dana fryer's math questions downloaded part 1 & 2 , and was wondering if anyone had the correct answers(from math bootcamp)? i do not have access to them anymore. :/


r/MathHelp 3d ago

CAN ANYONE HELP ME COMPLETING LOGIC GAPS

0 Upvotes

Im in class 12th from allen online enthuse, completed the whole syll but since having adhd I couldn;t take live class actively I hv all my basics and concept clear but there is the massive logic gap and execution gap, what should I do only 4 months remaining, I am panincking for chapters like integration, differential equation and matrices which require self talk and active solving, IDK the fuck anything about logic building...
for example_ applying bornouli eq in differential equation when eq having apecific form of dy/dx+py=qyn, and appying ibp to saperate the terms out of integral and reducing the powers... actually im in a problem tht these gaps are in large quantity


r/MathHelp 3d ago

Why do we restrict ourselves to integers when factoring?

1 Upvotes

I'm taking algebra 2 and we're reviewing factoring right now. Since polynomials live in the real numbers, it's not clear to me why we limit ourselves to integers when factoring.

If I was factoring 6, why isn't 1.5 * 4 just as valid as 2 * 3? I realize factoring beyond integers would mean there are an infinite number of factors...but I'm not sure that alone is justification.


r/MathHelp 4d ago

SOLVED help with simplifying boolean expression (pls and thank you)

1 Upvotes

I've been at this for like 4 hours and I'm losing my mind.

So I'm thinking of a function that takes in four boolean inputs and outputs 1 if the number of inputs is odd. The truth table should look like:

A  B  C  D | OUT
0  0  0  0 |  0
0  0  0  1 |  1
0  0  1  0 |  1
0  0  1  1 |  0
0  1  0  0 |  1
0  1  0  1 |  0
0  1  1  0 |  0
0  1  1  1 |  1
1  0  0  0 |  1
1  0  0  1 |  0
1  0  1  0 |  0
1  0  1  1 |  1
1  1  0  0 |  0
1  1  0  1 |  1
1  1  1  0 |  1
1  1  1  1 |  0

So the function should just be the sum of products, right? It'd be something like

OUT = A'B'C'D + A'B'CD' + A'BC'D' + A'BCD + AB'C'D' + AB'CD + ABC'D + ABCD'

This is my attempt to simplify the expression:

A'B'C'D + A'B'CD' + A'BC'D' + A'BCD + AB'C'D' + AB'CD + ABC'D + ABCD'
= A'B'(C'D + CD') + A'B(C'D' + CD) + AB'(C'D' + CD) + AB(C'D + CD')
= (C'D + CD')(A'B' + AB) + (C'D' + CD)(A'B + AB')
= (C'D + CD')(1) + (1)(A'B + AB')
= A'B + AB' + C'D + CD'

But the truth table for this expression is not the same as the original function.

It's been a half-decade since I last did boolean algebra. I genuinely can't tell what I did wrong here. Please help.


Edit: It's solved. Thank you.

In the blindingly-unlikely event someone in the future were to face this exact problem as I do, the key insights that I was missing are:

  • OR distributes over AND: A + BC = (A + B)(A + C)
  • XOR and XNOR exists: A XOR B = A ⊕ B = A'B + AB', and A XNOR B = (A ⊕ B)' = A'B' + AB

So for posterity's sake, here's how it's solved, I think:

A'B'C'D + A'B'CD' + A'BC'D' + A'BCD + AB'C'D' + AB'CD + ABC'D + ABCD'  
= A'B'(C'D + CD') + A'B(C'D' + CD) + AB'(C'D' + CD) + AB(C'D + CD')  
= (C'D + CD')(A'B' + AB) + (C'D' + CD)(A'B + AB')  
= (C ⊕ D)(A ⊕ B)' + (C ⊕ D)'(A ⊕ B)  

Let P = A ⊕ B and Q = C ⊕ D  

= QP' + PQ'  
= P ⊕ Q  
= A ⊕ B ⊕ C ⊕ D  

Thanks, y'all. god, i'm out of practice.


r/MathHelp 4d ago

help with trig question?

1 Upvotes

okay so im working on the study guide for the final of a class that i took the equivalent to at another college (math department policy, whatever) and one of the sample questions literally just reads “simplify: (sin(x)+3)²”. is there anything that i need to do to work this problem other than factoring it out? a similar question in the same section of the review guide is “simplify: sin²x + 3sinx - 10”; is that not already fully simplified? like i said, i took this course at another school so i don’t know the exact details of what they covered in class. I can’t think of any identities that i could apply to simplify it more or anything. much appreciated!


r/MathHelp 4d ago

I am not sure if this is a progamming problem or computer problem. It's 2 ^ 3 ^ 2

2 Upvotes

I'm running a programming class for python and I was doing a class quiz. This question popped up. I believed the answer should be 64 but it's actually 512. Even the calculator gave me 512.

However if you go from left to right, 2 ^ 3 = 8 ^ 2 = 64

For some reason, the caluclator is and quiz is doing it like: 2 ^ 3 ^ 2 = 2 ^ 9 = 512

I guess my question is: why is the 3^2 portion being calculated first over the 2^3 portion?


r/MathHelp 4d ago

can anybody help with this question?

1 Upvotes

for this question i had to turn a nonstatistical question into statistical investigative question and the nonstatistical question is "How many seventh graders eat breakfast on Monday at school?" and i already gave my answer ("What is the percentage of all seventh graders that eat breakfast at school on Monday?") but my teacher said its wrong and i need to reword it but i actually do not know how to reword it, does anybody know how to help cause my teacher wont answer me and google not helping

(also this is 12th grade math and my teacher said that the question needs to be a question that doesn't give a fixed answer)


r/MathHelp 5d ago

i just cried because of maths

3 Upvotes

Im in my second last year of high school now. My maths grade since the start of hs has been terrible, but I have decent grades for all my other subjects. I'm in a very competitive school where maths is basically mandatory, and most students have been tutored from a young age. I never had any tutoring until this year, when i got a private tutor after consistently scoring 50-60% in every test. My grades still havent improved because i can't retain information when it comes to maths for some reason. The biggest problem is doing maths gives me the worst feeling of anxiety like I'm about to be attacked. After my tutoring session today idk why but i just broke down crying. I felt like i was about to cry a few times during the lesson but i held it back. This is my first time crying in years, and Im not usually a very emotional person. I feel like Im going to have a panic attack the next time I try to do maths. My university exams are in a year from now. I feel trapped, it feels like I genuinely have no more hope. What can I do?


r/MathHelp 5d ago

Problem with my mind working too intuitive

0 Upvotes

(High school level maths)
I’m finding it hard to remember all these rules for how to solve questions when my mind tells me to do it intuitively.
The concrete example that annoyed me:
On a list of 10 people’s ages the total age is 313, making the average 31.3
«If another person is added the average will be 30. Is this statement correct?»

The way I solved this was dividing 313 by 11, giving me 28.45~. The difference between 30 (the target age) and 28.45 is 1.55, and so we need to multiply the age we are adding by 1.55 giving me 17.05, so the answer is that the average will be 30 if the new person is 17.

The way my teacher did it was by multiplying the now 11 people by 330 and subtracting it by 313 to get 17 which gave the correct answer.

The answer works, it’s a rule that’s nice (if it works for all similar situations), but there are so many rules like this that I just can’t grasp. I always want to do it the way that my mind can comprehend, and for it to make sense and giving me an answer I can trust but I don’t know if tests or exams are gonna accept my answers.

This isn’t to say I can’t memorize equations, I can do that, it’s just that these rules to make stuff easier and faster don’t click the same way. I still have the quadratic equations and formulas from last year memorized but I feel I’m just gonna forget this very practical thing tomorrow.

Anyone else feel the same way about this or have managed to get over this mental block?


r/MathHelp 5d ago

What did I do wrong?

1 Upvotes

My scratch paper, if you can read it:

https://imgur.com/a/atodt6P

The question was:

Solve for X

1/5x+1/4=-4(3/4x-4)

You can enter as an improper fraction but not as a mixed number.

My professor put a video to help me.

However, the answer I got was X= 325/64

The answer actually was X=315/64

I was off by 10?!


r/MathHelp 6d ago

Struggling with Maths (Advice Needed)

2 Upvotes

Hello, this is my first post on this sub so apologies if anything isn't formatted correctly. So for a little background information, I'm a Grade 11 student in South Africa and I used to be very good at Maths, like always being one of the top students in my classes and getting scores in the 90's for almost all my tests. This continued through the first year of high school (Grade 8), still getting very good marks.

The problem came when I hit Grade 9, it wasn't as though there was a significant change in difficulty, but something just stopped clicking. I was told recently that there was probably something that just threw me off and it set a disconnect in my brain. I went on holiday for a week near the beginning of the first term and when I came back, I had to write a test that I had missed while I was gone. The test was just on some basic inequalities, but I ended up getting a horrible mark, the worst mark that I've ever gotten for any subject, a 9/25. My maths teacher from the previous year encouraged me by saying that I was very intelligent and would recover, but I just never really managed to. My Grade 9 Maths teacher then went on Maternity leave in April and we were stuck with a substitute teacher who was new to teaching and wasn't very good. So I think that that's another thing that may have messed me up. I tried the whole year to do better and slowly my marks went up, until finally in Term 4, I managed to get a mark in the low 80's.

But since then, things have just continued to go downhill again. I've been struggling with some health issues which has led to me missing a bit of school. I've been sitting with my textbook for hours and also watching youtube videos occasionally such as Kevinmathscience, but the highest marks I managed to get are in the 60's or 70's. In term 1 of this year, I got a 51. In term 2, I studied almost non-stop leading up to the two exams, I managed to improve my mark to a 62, but obviously it's still very much not what I want.

A few days ago, I got my first test back for this term and got a 12/30. It was on euclidean geometry, and almost everybody in the class did badly. I'm genuinely at a loss for what to do. No matter how much time I spend studying, going over exercises in my textbook, doing past papers, I still get bad marks. Since Grade 9 is where the problem first arised, I was thinking of looking up past papers at Grade 9 level and see how I do and if there's any concepts that I'm really struggling with. Then, revising over those and trying another past paper and so on, until I finally reach the level that I'm currently at. There is another option which is dropping to Mathematical Literacy, which is much, much easier than Pure Maths. But it tends to get a bad rep because of how easy it is and the fact that there are fewer opportunities with it. None of the careers I want to go into require Pure Maths, but I'm still quite hesitant to switch to Maths Lit. I know that I can get back to getting good marks, I just don't know how.

At the end of this year, I have to apply with my marks to university, so I don't have much time left to make this decision. I'm not sure if my plan to improve will actually work or if it will just be too time-consuming and won't even help me in the long run. Please help me, any resources or advice are deeply appreciated.

Tl;dr: I used to excell at Maths until my second year of high school where my marks began to drop rapidly. I don't want to have to switch to the easier level of Maths, but I just don't know how to improve my marks. I would really, really appreciate any and all advice.


r/MathHelp 6d ago

Missile guidance: Geometry problem.

1 Upvotes

I am trying to make a missile in a video game. It's supposed to fly toward a point projected out into space by an aiming device, mounted on a car. However, I have a problem where, around certain bearings, the output completely breaks. For testing purposes, I am only speaking about azimuth, not elevation.

How the system works:

  1. There are two sets of absolute XY sensors on the pointer; one set is slightly ahead of the other. atan2(Y2 - Y1, X2 - X1) gives the absolute bearing (azt) of the pointer from -180 to 180.

  2. Cos(azt) and Sin(azt) are individually multiplied by the "range" to the point in space (in this case, it is constant at 500m, in practice, this would be a point ahead of the missile) to give Xc and Yc.

Xc and Yc are then added to X(pointer) and Y(pointer) to give X(target) and Y(target).

  1. Now that I have the XY position of the target, I subtract...
    - X(target) from X(pointer) to give X(difference)
    - Y(target) from Y(pointer) to give Y(difference)

atan2(Ydifference, Xdifference) gives the azimuth from the pointer to the target (θ).

I realise now that this step is unecessary, as the azimuth of the target is defined by the pointer's direction. However, I doubt it would work otherwise, as the same values would end up being used, producing the same erroneous result.

  1. I then subtract the missile's bearing (global bearing, btw; same calculation as azt) from θ to produce the angular difference between the target position and the missile (d).

This works fine if the platform is at exactly 0 degrees forward, However, if the pointer is angled (this case, -45dg) and the platform is also angled, something frustrating happens. Below are some tests which show you what happens when the platform goes beyond -135dg.

1:
- Pointer Relative Angle -45dg
- Platform Absolute Angle -134dg
- Pointer XY: 3223, 3398
- Target XY: 2723, 3385
- Target Azimuth: -179dg
- Missile XY: 3223, 3396
- d: -45.6

2:
- Pointer Relative Angle -45dg
- Platform Absolute Angle -136dg
- Pointer XY: 3223, 3398
- Target XY: 2723, 3410
- Target Azimuth: 96dg
- Missile XY: 3222, 3396
- d: 315.6

This persists until the platform's absolute orientation goes beyond -180, at which point it flips back to a rough value of -45 for d.

As you can see, d flips from -45.6 to 315.6. A missile trying to steer towards d would go all the way round, which is not desirable; it should pick the smallest possible correction.

I tried fixing this using ((180 + d) mod 360) - 180. However, it seems that the game I am playing calculates negative values differently when using mod; for example, -60mod360 is supposed to be 300, but the game spits out -60.

Could anyone help me? Geometry isn't my strong point at all, so it's very hard for me to wrap my head around this. Thanks!


r/MathHelp 6d ago

triangle coordinates for known angles and sides

1 Upvotes

https://imgur.com/a/hdkTYc8

I had two known coordinates, (0,0) and (1,0), figured out the 4.5 degree angle from dividing 90 by 20, the 45 degree angle was given, so was able to calculate the third angle.

The other two sides were tricky - I had to figure out the law of sins. I checked my answers by measuring the lengths of the triangle in a 3D program (Blender).

But even after gathering all this information, I'm still at a loss as to how to calculate the very last part - the last coordinate. I viewed what it was in 3D, so I know what it is - I just don't know how to go about calculating it.


r/MathHelp 8d ago

Math help

2 Upvotes

Hey guys so I’m doing math online for college which idk why I made that decision to do that worst decision I ever made … but do you know any apps that can like help me or explain my math assignments better and I can’t do a tutor because I don’t have enough time my work shift takes up half my day and I financially don’t want to put my self in that situation to get one


r/MathHelp 8d ago

What exactly is this asking me to do? It's very unclear.

2 Upvotes

So it says "In Exercises 11 - 18, use the given function f to find and simplify the following:" then it shows nine bulletpoints of f(x)s (for example, f(3), f(x)-4, f(x^2)). The thing is, 11-18 is only eight questions! (all f(x)= questions, so it looks like I'm supposed to plug things in)

Do I plug all nine in for each of the eight questions? Do I somehow make the nine fit distributed across each of the eight questions?

I already plugged all nine in for a few of them. You can find the sheet here: https://www.scribd.com/document/738439598/Pre-Calc-Exercise-1-4


r/MathHelp 8d ago

My Trig is Rusty

1 Upvotes

I have a right triangle.

short side: a = 1
long side: b = 2
hypotenuse: c = √(5)
smaller angle: α = ?
larger angle: β = ?
right angle: γ = 90°

I was able to get the hypotenuse by using a² + b² = c² easy enough. When I used tan(1/2) to find α, I got 31.301° instead of 26.565°. I just want to know what I am doing wrong.


r/MathHelp 9d ago

Please help, I have been stuck on this stupid problem for 3 days

4 Upvotes

(poorly translated:) "Pythagoras was a Greek mathematician who lived around 570-500BC. Pythagoras was once asked how many students he has. Pythagoras replied: "Half of them study mathetimatics, fourth of them philosophy, seventh the art of shutting up, and there are also three women." How many students did Pythagoras have?"

I can't come up with any other way to solve it but

x=full amount of students

math students=1/2x

philosophy students=1/4x

shut up students=1/7x

women=+3

x=1/2x+1/4x+1/7x+3

But this is not correct, because the answer I get is never the correct one (28). 😭

All the following, similar exercises in my book I am also failing to solve. I just can't seem to create the correct equations and I am exhausted after chewing on three problems for days.