Draw a hypocycloid using a graphical calculator (such as Desmos or Geogebra).

Your hypocycloid should include

• Inner circle of radius `a
• Outer circle of radius `b
• As time t increases the point on the inner circle should trace out the pattern, you can animate the graph using t.

Below is the link to a Desmos graph:

https://www.desmos.com/calculator/vzgog7xqrz

• Given n and m are coprime, show that there exist integer n' such that nn' mod m=1.
• The extended Euclid's algorithm is given below without proof, which may be useful in your proof.

(I'm too lazy to type out the algorithm again, so look at the image yourself)

• Prove that z(x mod y) = (zx) mod (zy)

Be rigorous

(trust me bro im gonna daily post trust me bro)

EDIT: assume all variables are integers

I recently started reading TAOCP, in other words you can expect daily posts from me again, because I'll just take some of the cooler questions from there and repost them here.

S=sum of (-1)^n/n from 1 to infty

For why I named the post as so, here's why

This is related to the the May 16 post, but takes only the prime indexed terms. Does it still diverge?

• Show that cosθ=(u⋅v)/(|u||v|) for 2D vectors u and v.

(it is quite hard to come up with these challenges, so if you got any ideas, please post them)

We're playing a game. I flip a coin. If it lands on Tails, I flip it again. If it lands on Heads, the game ends.

You win if the game ends on an even turn, and lose otherwise.

Define the following events:

A: You win the game

B: The game goes on for at least 4 turns

C: The game goes on for at least 5 turns

What are P(A), P(B), and P\(C)? Are A and B independent? How about A and C?

It is not

Consider the function defined by y = x\^(sin(x)\sin(x)). Observe its graph. Find an increasing function which passes through each of its local maximums, and another increasing function which passes through each of its local minimums.

Extra credit: You'll notice the graph isn't drawn for x-values which make sin(x) negative. This is because most of those values make the function undefined - though it is defined for infinitely many points in those intervals, it just also has infinitely many holes. Since it lacks continuity here, it has no true local maxes or local mins, and doesn't impact the original problem. We can nonetheless cheat and fill in the holes by expanding the function to these regions with y = x\^|sin(x)|\sin(x) (Using x\^-|sin(x)|\sin(x) should also be technically valid, but is being ignored because it's discontinuous with the rest of the graph and not as pretty, but will be mentioned in my solution). Doing so adds more local maxes and local mins. The new local mins should line up with your function that finds the local maxes for the original function - but, find a new function which hits all of the new local maxes.

I've even got a starter question to get you guys into the scenario.

Once you've completed the starter question, under the solution comment attaches the main question, which is unsolved.

• Show that the infinite multiplication (1+1/1)(1+1/2)(1+1/3)... does not converge.

• Show that if a function is differentiable for an interval, it is continuous over that interval.
• A function is continuous if lim_x->a f(x) = f(a)

(x/5)\^log_b(5) - (x/6)\^log_b(6) = 0

• Express y in terms of x for differential equation dy/dx=ylny

(I'm officially out of ideas again)

• Show that it's possible a^b=c where a and b are irrational, and c is rational.

Sry for the gap I ran out of ideas.

• Show that the sum of the first n squares is n(n+1)(2n+1)/6.
• I know this is often in the textbook for proof by induction, which is why proof by induction is not allowed.

This is a relatively hard one, take your time.

Index of my unnamed series of posted problems

|Date|Post |---|---| |2024-05-07 | Find a+b |2024-05-09 | What is the area of the shaded region? |2024-05-15 | Solve for x |2024-05-17 | Bounding a function |2024-05-22 | Coin-flipping game

An 8x5 rectangle. If the bottom left corner is considered (0, 0), then two lines are drawn within the rectangle, from (0, 4) to (8, 1) and from (1, 5) to (7, 0). The smaller two regions of the four these lines cut the rectangle into are shaded. What is their combined area?

• Evaluate SUM(1/(n + n^2)) from n = 1 to infty

• Show that arcsin y = arccos x is the equation of a circle.
• Note that the equation of a circle is x^2+y^2=1.

!

The image is of a large unit square with five smaller disjoint shaded squares contained entirely within it. The five smaller squares are congruent. Four of them are at each corner of the large square. The fifth is in the center, rotated diagonally, so the center of each of its sides is touched by the vertex from one of the other four squares. You are given that the common length for the five smaller congruent squares is (a-sqrt(2)) / b, where a and b are positive integers. What is the value of a + b?

• Solve x for x^x*x\x^ = 2
• Note that the Lambert W function W(x) is the inverse of f(x) = xe^x

Prove L'Hopital's rule, nothing fancy.

Find x for x^xx^xx^... = 2

Prove that the sum of the reciprocals of the Fibonacci numbers up to infinity converges to a finite value.

Find ∫e^x sin⁡x dx.

Active series

|No. of posts|Name|Frequency|Difficulty| |---|---|---|---| |22|Siri's Medium|Daily|5/10| |5|zkfcfbzr's unamed series|Irregular|4/10|

If you want to start your own challenge series, create an index post like this one, and let me know in the comments.

Resources

• Discord bot to mirror posts in this community using RSS.
• KaTeX so you can include a screenshot of your maths.

Index of Siri's Challenges

|Date|Post|Difficulty| |---|---|---| |2024/08/07| Hypocycloid|7/10| |2024/08/04| Extended Euclid's algorithm|6/10| |2024/08/01| Multiple of modulus|6/10| |2024/06/28| Approximate log base 2|5/10| |2024/06/02| Horizontal asymptote of the other kind|7/10| |2024/05/25| Angle between two vectors|7/10| |2024/05/17| [Unsolved] 1 dimensional gravity|9/10| |2024/05/16| Infinite multiplication series|5/10| |2024/05/15| Differentiability implies continuity|6/10| |2024/05/14| General differential equation|4/10| |2024/05/13| Irrational powers |5/10| |2024/05/09| Sum of n squares |8/10| |2024/05/08| Definition of e^x |5/10| |2024/05/07| Evaluate converging sum |5/10| |2024/05/06| Equation of circle |4/10| |2024/05/05| Fake power tower |7/10| |2024/05/04| Prove L'Hopital's rule |6/10| |2024/05/03| Infinite exponential |5/10| |2024/05/02| Reciprocals of Fibonacci numbers|5/10| |2024/05/01| Integral of e^x sinx|5/10| |2024/04/29| Approximate 10000 factorial|8/10| |2024/04/28| Sum to infinity is -1/12|7/10|

If you got any good ideas, PLEASE PM ME I can't come up with that many challenges that quickly.

• Estimate 10000!
• Give our answer in form exp{a ln(a) - b ln(b) + c}
• Hint: e

• Proof that the infinite sum 1+2+3+4+... = -1/12
• You may assume that 1-1+1-1+... = 0.5