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 90 How to find a general sum formula for the series: 5+55+555+5555+…? 12 How many pairs of positive integers $(x,y)$ satisfy the equation $x^2 - 10! = y^2$? 7 Is $e^{i+\pi}$ irrational or not? 5 How to find the general formula for this recursive problem? 5 Integer solutions to $a^{2014} +2015\cdot b! = 2014^{2015}$

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 3 trigonometry equation $3\cos(x)^2 = \sin(x)^2$ 2 What is Odin's present age? 2 trigonometry equation, $[\cos(2x)]^2-\sin(2x)=1$ 2 Find $\lim_{x \to 0}\frac{\cos 2x-1}{\cos x-1}$ without L'Hopital's rule. 1 Proving $\left(1-\cos^2x\right)\left(1+\tan^2x\right)=\tan^2x$

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 9 trigonometry × 9 1 combinatorics × 8 2 calculus × 4 1 arithmetic × 2 2 algebra-precalculus × 3 1 exponentiation × 2 2 limits × 2 0 triangles × 10 2 limits-without-lhopital × 2 0 sequences-and-series × 8

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