Top network posts
- 6 Olympiad question: In the regular pentagon $ABCDE$, the perpendicular at $C$ to $CD$ meets $AB$ at $F$. Prove that $AE + AF = BE$.
- 5 What is $x$, if $1! + 2! + 3! + \cdots + (x-1)! + x! = k^2$ and $k$ is an integer?
- 5 How to solve this problem without using the binomial expansion?
- View more network posts →