Beautiful, simple proofs worthy of writing on this beautiful glass door [closed]
Solution 1:
Barak beat me to my #1 choice. This would be second:
Solution 2:
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$\qquad\qquad\qquad\qquad\quad$ Geometric Explanation of the Binomial Theorem
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$\qquad\qquad\qquad\qquad\qquad\qquad\qquad$ Proof that $~\displaystyle\sum_{k=1}^n(2k-1)=n^2$
Solution 3:
Cosines and Sines Around the Unit Circle
Trigonometric Angle Sum and Difference
Solution 4:
For me, it's Conway's inverse proof of the Morley equilateral triangle:
