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) }}}.

Algebra ->  Trigonometry-basics -> 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) }}}.      Log On


   

Question 1110430: If , evaluate +cos%5E2+%28pi%2F9%29%2Bcos%5E2+%282pi%2F9%29%2Bcos%5E2%283pi%2F9%29%2Bcos%5E2%284pi%2F9%29+.
Answer by ikleyn(52850) About Me  (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.