Skip to main content
peterwhy's user avatar
peterwhy's user avatar
peterwhy's user avatar
peterwhy
  • Member for 10 years, 10 months
  • Last seen this week
73 votes

Has anyone heard of this maths formula and where can I find the proof to check my proof is correct? $\sum^n_{i = 1}i + \sum^{n-1}_{i=1}i = n^2$

44 votes

Inequality with square roots: $\sqrt{x^2+1}+\sqrt{y^2+1}\ge \sqrt{5}$

19 votes

Alternate ways to prove that $4$ divides $5^n-1$

18 votes

How to evaluate $(0.9)^4$ without calculator

18 votes

Prove that the square of any given odd number gives a remainder of 1 when divided by 4

17 votes

The milk sharing problem

16 votes
Accepted

Probability question about cherry picking

14 votes
Accepted

How to fold a4 paper for 30 degree angle?

14 votes

Inequality with square roots: $\sqrt{x^2+1}+\sqrt{y^2+1}\ge \sqrt{5}$

14 votes

Alternate ways to prove that $4$ divides $5^n-1$

12 votes
Accepted

Question on series till 2009

11 votes
Accepted

The behavior of quadratic formula in the limit $a\to 0$

11 votes

Prove that $x^2 + xy + y^2 \ge 0$ by contradiction

11 votes

What is the name of this curve?

10 votes

Prove that $ ax^2+bx+c=0 $ has at least one root in $(0,1)$ if $10a+12b+15c=0$

10 votes
Accepted

Proof by induction, factorials and exponents

10 votes
Accepted

Quadrilateral in which diagonal is partially outside?

9 votes

Applying theorems and properties to solve indeterminate limits

8 votes

Why do we choose only the positive sign when substituting $x=\sin(t)$ into $\int \sqrt{1-x^2}\,\mathrm dx\;?$

8 votes

When studying a book (like Rudin ) where the problems are not intended to be fully solvable by a student, what criteria show you're ready to advance?

8 votes
Accepted

When does a function NOT have an antiderivative?

8 votes
Accepted

General formula for a sum of quadratic sequence

8 votes

Solve $\sin2x +\sin x = 0$ algebraically

8 votes

A series for Fibonacci numbers.

8 votes
Accepted

How to solve "$4\sqrt5$ is the same as which square root?"?

8 votes

Induction without a base case

7 votes

Prove that if $n > 4$ is composite $n|(n-1)!$

7 votes

how to integrate (x-1)/(x+1)

7 votes
Accepted

How to integrate following indefinite integal?

7 votes

Why are $x$, $x^3+1$ and $x^2+x+1$ always mutually co-prime, for any natural number $x$?

1
2 3 4 5
29