What a nice cosines sum!

Geometry Level 3

If cos 2 ( 1 ˚ ) + cos 2 ( 2 ˚ ) + cos 2 ( 3 ˚ ) + + cos 2 ( 90 ˚ ) = a b , \large{\displaystyle \cos^2(1˚)+\cos^2(2˚)+\cos^2(3˚)+\dots+\cos^2(90˚)=\frac{a}{b}}, where a a and b b are positive co-prime integers, find a + b a+b .


The answer is 91.

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1 solution

Raj Rajput
Jul 30, 2015

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