Basel's Problem

$$1+\frac{1}{4}+\frac{1}{9}+\cdots = \sum_{n=1}^{\infty}\frac{1}{n^2}=\frac{\pi ^2}{6}$$



Now you might be thinking - "How on earth are they even related!!"

Well the reasoning is a bit too long to write it all out in this one post.
I suggest you have a look at this brilliant article by Mikael Passare -How to Compute $\sum_{n=1}^{\infty}\frac{1}{n^2}$ by Solving Triangles 

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