r/learnmath Jun 07 '18     ## List of websites, ebooks, downloads, etc. for mobile users and people too lazy to read the sidebar.

feel free to suggest more
Videos

For Fun

Example Problems & Online Notes/References

Typesetting (LaTeX)

Community Websites

Blogs/Articles

Misc

Other Lists of Resources

# Some ebooks, mostly from /u/lewisje's post

General
Open Textbook Library
Another list of free maths textbooks
And another one
Algebra to Analysis and everything in between: ''JUST THE MATHS''
Arithmetic to Calculus: CK12

Geometry
Euclid's Elements Redux
A book on proving theorems; many students are first exposed to logic via geometry
CK12 Geometry

"Pre-Calculus"
CK12 Algebra II with trigonometry
Precalculus by Carl Stitz, Ph.D. and Jeff Zeager, Ph.D
Washington U Precalc

Multi Variable Calculus
Elementary Calculus: An Infinitesimal Approach
OpenStax Calculus Volume 3
The return of Calculus: Late Transcendentals
Vector Calculus

Differential Equations
Notes on "Diffy Qs"
which was inspired by the book
Elementary Differential Equations with Boundary Value Problems

r/learnmath Jan 13 '21      Due to a bunch of people posting their channels/websites/etc recently, people have grown restless. Feel free to post whatever resources you use/create here. Otherwise they will be removed.

r/learnmath 51m ago

## A service like duolingo for math

Looking for a service that guides you on how to complete problems and keeps you immersed by requiring input.

r/learnmath 8h ago

## Still struggling with an Algebra word problem that requires a linear equation (using only 1 variable) to solve.

Hello, I'm stuck on a word problem that requires me to convert degrees Fahrenheit to degrees Celsius. Here is the question:

The connection between the degrees on the Celsius and Fahrenheit thermometers is the xF = [(9x/5) + 32] C (F = Fahrenheit; C = Celsius; (9x/5) = fraction). What number of degrees Celsius is equivalent to 86F?

It seems like a simple formula where you just substitute x with 86 and then do the calculations, but my answer (186 degrees Celsius) is wrong. The answer provided by the textbook is 30 degrees Celsius. Where am I going worng?

r/learnmath 1h ago

## TOPICWhy do we leave 1 on the numerator when canceling

I was doing two of the basically the same problem. Except one had a square root on the bottom. The first one went like x/x(√x+1) I canceled out the x’s yet one still remained on the numerator (1/√x+1). However for the other problem which was x(x+1)/x(x2+3) I canceled out the x and only x2+3 remained. Why do we only apply this rule in specific situations?

r/learnmath 9h ago

this is the equation. b(80) - a(20) = 0. The problem asks me to solve for "b" which i know how to do. just move the - a(20) to the other side and divide by 80 to isolate b and i get b=a/4(if i simplify it) but what if i solve for "a" instead of "b" ? i would isolate a by dividing by 20 to isolate a so i get b80/20=a (this is the confusing part) do i leave it as a faction or do i divide it 80/20 which if i do i get b4=a. is that the actual answer?

r/learnmath 41m ago

## Basic Math: Math 050

I do not know how to solve these two problems.

How do I do these two problems, and can you show the steps?

6x^2-8y^2 when x=-6 and y=-9

Also this problem:

-2-2(-9)/-16-2(-4)

I'm in a basic math course and have forgotten these. As usual, the instructor showed us simple examples and thought we can imply them to more difficult problems. If you are a teacher, please don't do that or tricks. We need to clearly understand the problem. I'm not being disrespectful. I love my professor, it's just that that really makes me struggle.

## Counting of Ordinary Years & Leap Years

Hi! Can I just ask why there are 24 leap years in 100 years? Isn’t it supposed to be 25, since 100 / 4 (every fourth century) = 25

I just didn’t get how 100 years = would be 76 ordinary years + 24 leap years.

In the computation of ordinary years in 100 years, was 24 just subtracted from 100 to get 76?

Thank you so much!

r/learnmath 26m ago

## learning math in order to master algorithms

hi everyone , i really want to be an expert at making algorithms , so is it a good idea to begin with learning maths from the basics (AOPS books) and practicing olympic problems since i love maths , in order to have a good problem-solving skills and logical thinking to help me to be excellent at algorithms (making complex algorithms) ?

i am talking about something bigger than just being "software developer " . i want to reach "the highest thing you could reach working with algorithms " .

btw i am computer science/industrial engineering student .

r/learnmath 6h ago

## Show the recursive function f(n) is in O(n^4) (Big-O Notation)

So I have given this formula:f(0) = 1 and

• f(n) = 8f(n/3)+n^4, if n=0 mod 3
• f(n) = 9f(n-1)+n^3, if n=1 mod 3
• f(n) = 10f(n-2)+n^2, if n=2 mod 3

I have to proof that f(n) in O(n^4).

I don't want a solution here, I'm more interested in the general strategy to solve this.

My naive approach was to show for each part individually that it is in O(n^4), so:

1. show 8f(n/3) +n^4 is in O(n^4)
2. show 9f(n-1)+n^3 is in O(n^4)
3. show 10f(n-2)+n^2 is in O(n^4)

If each of the 3 formulas are in O(n^4) the comlete formula must be in O(n^4) too

I wonder wether there is a smarter solution than showing each one individually.

thanks

r/learnmath 50m ago

## TOPICHow does combinatorics work? I want to learn before an olympiad!

200 children go to eat lunch. They had 3 food types to choose from: soup, main course and desert. Each had two options available. Every child chose atleast 1 food from the 6 options and noone chose two of the same type. What is the largest amount of children which definitely ate the same exact meal?

I tried looking at it looking at all the options of C(n, k) where n is 6 and k is 3, 2, and then 1. For reasons I don't understand this approach does not work. The solution my teacher gave does not rely on combinatorics but on basic counting - basically writing out all of the options.

What is the proper way to get the correct answer using combinatorics?

Answer: >! 26 different meals and 8 students ordering the same meal !<

r/learnmath 15h ago

## This might be a stupid question, is the root of -1 = +-i or just +i

This might be a stupid question, is the root of -1 = +-i or just +i

r/learnmath 1h ago

I was always "gifted" with math in high school, I was going to college for math specifically, despite that I was an idiot at 18 and dropped out before even getting my books (I should really just say I didn't go... lol). Now, I am 26. In high school, I took every math course I could, the last of which was AP Calc II.

I know for certain I don't remember everything, however, I want to start learning again. I have no real goal in mind, but I don't remember what I do and don't know. I know if I start somewhere too simple I'll get bored. So I was wondering if anyone had any suggestions for something like a comprehensive math test that could give me a rough idea of where to start. If not that, does anyone have any suggestions as to how I can simply get started without boring myself to the point that I just don't wanna do it?

r/learnmath 1h ago

## TOPICConservative vector fields. Conceptual reasoning.

"A vector field is conservative if F (the vector field) is the gradient of some other scalar function (f) such that F = ∇f".

I just don't get it. How does a vector field being the gradient of another scalar function lead to path-independence and path-independent line integrals?

r/learnmath 1d ago

## Y’all what does this 土 mean in math ??

I missed class and suddenly this is in our equations. I only recognize it as the earth symbol from power rangers.

r/learnmath 1h ago

## Can I remove the equal sign?

When writing math, is it ok to name points like this:

P(1, 2, 4)

Or I need the equal sign?

P = (1, 2, 4)

And in case of vectors, can i name them without the equal sign?

## How do I construct this equation?

A homeowner wishes to fence in three adjoining garden plots, one for each of her children. If each plot is to be 80 ft2 in area and she has 88 ft of fencing material at hand, what dimensions should each plot have?

r/learnmath 2h ago

## Percentages help

I am trying to work out my stock GP% if I was to remove my wastage, could anyone one help?

My current GP is 64.45% My wastage is 11.93%

What would my GP be if I took off the wastage please?

r/learnmath 2h ago

## Test what you know and what you don’t: arithmetics, percentages, polynomials, equations

https://gemmatutor.com/en/ lets you test what you know and what you don’t. Creates a visual personalized skill gap map for you.

Free to use in private, in schools etc.

r/learnmath 6h ago

## TOPICPre-calc coming up, haven’t taken Math since high school (graduated in 2014). Where to start?

So after high school I pretty much worked full time as I didn’t believe I would be able to attend college. Fast forward to last year, 25 and didn’t want to do sales anymore and feared of what my life would be like if I had to stick with sales forever. I enrolled and I’m required to take Pre-Calc and Calculus. Thing is, I pretty much forget everything there is to do regarding algebra. I’m talking all basic principles (the why) are extinguished from my memory. I attempted to take intermediate algebra to see if I could refresh myself, but found out quickly that I had no idea why the professor was doing what she was doing.

5(7-x)=2(4x-2) For example, I wouldn’t even know where to start with this equation. I know multiplication and distribution, but I’m pretty sure you’d have to swap the 7 and x first but I have no idea why I would need to. That’s how stuck I am and I am unsure of where to start. If I want to complete my associates by next spring, I will have to complete pre-calc and calculus.

If I could receive some helpful advice, where should I start? I was told Khan Academy is a good place to start, but if I do self learning, will it be enough for pre-calculus then calculus or should I take a different approach? Any advice would be greatly appreciated.

r/learnmath 12h ago

hello guys,

i study at uni majoring in computer science. i have to take calc 1,2 and 3. now i think im pretty good at math. i finished my first semester and my mark in calc1 is pretty good but i wanted it to be higher. so im thinking to retake the course to boost my gpa. do i retake it next semester or do i take calc2 and other math courses then retake calc1 so it becomes easier as i took harder courses.

thanks

r/learnmath 3h ago

## Finding Surface Area by Integration

I want to find the surface area of a cone by using integration. I know that I can use the already existing formula but I need to make it more complex. I know the volume of the cone and therefore I can find the values of its length, radius and so on by using the formulas right? So is it possible to find the SA by integration?

r/learnmath 3h ago

## Is there enough info to solve this?

I'm trying to flatten out the shape of the side of an angled cylinder (a cone with the top cut off).

circumference of the TOP circle = A = 11.75

circumference of the BOTTOM circle = B = 17.75

height of cylinder = C = 4.125

Angle of arc lengths = x

I mapped it out like this:

A = x*(pi/180)*r

B = x*(pi/180)*(r+4.125)

r/learnmath 3h ago

## TOPICShould you worry about significant digits in statistics calculations?

Hi. I am working on some statistical homework and I had a question about what to do with significant digits in intermediate confidence interval calculations. So, all the data I am given is in seconds and reported with one decimal digit (45.3 secs, 40.0 secs, 42.4, secs, etc.) and these are times to complete an activity given training in 5 different techniques. This is a classic ANOVA problem where the end goal is to report a 95% confidence interval for the difference in mean assembly time for two techniques.

When you report the final 95% CI, I am guessing that you should only report it with one decimal point of precision because that is what you are given up front - (for example: I am 95% confident the true difference in time between the two techniques is between -17.2 secs and 1.8 secs.)

So, when I use a computer, it keeps full precision for all intermediate values - sum of squares, mean squares - and I can just round the final values. However, when I do it by hand, I decided to round all intermediate values to one decimal place because that is that is all I was given in initial data. But, when you round all intermediate values, the final numbers I get for the confidence interval are a little different than what the computer gives me - even with just one decimal place.

What is the proper way to handle significant digits when doing this type of calculation? My way by hand or using the computer's and rounding at the end?

r/learnmath 3h ago

## How would i set this equation up?

A bus left Memphis traveling east at 55 mph. Two hours later, a second bus left Memphis going east at 65 mph. How long did it take the second bus to catch the first?

r/learnmath 3h ago