SOLUTION: If {{{sin^2 (pi/9)+sin^2 (2pi/9)+sin^2 (3pi/9)+sin^2(4pi/9)=9/4 }}}, evaluate {{{ cos^2 (pi/9)+cos^2 (2pi/9)+cos^2(3pi/9)+cos^2(4pi/9) }}}.

SOLUTION: If {{{sin^2 (pi/9)+sin^2 (2pi/9)+sin^2 (3pi/9)+sin^2(4pi/9)=9/4 }}}, evaluate {{{ cos^2 (pi/9)+cos^2 (2pi/9)+cos^2(3pi/9)+cos^2(4pi/9) }}}.

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Question 1110430: If , evaluate .
Answer by ikleyn(52858) (Show Source): You can put this solution on YOUR website!
.

Replace each sin^2 by the corresponding  1 - cos^2.


After that completing the assignment is pure mechanical work.

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