Question 1191167
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{{{ sin^2(pi/9) +  sin^2(2pi/9) + sin^2(3pi/9) + sin^2(4pi/9)=(1- cos^2(pi/9)) +  (1-cos^2(2pi/9)) + (1-cos^2(3pi/9)) + (1-cos^2(4pi/9))}}}<br>
{{{9/4 = (1- cos^2(pi/9)) +  (1-cos^2(2pi/9)) + (1-cos^2(3pi/9)) + (1-cos^2(4pi/9))}}}<br>
{{{ cos^2(pi/9) +  cos^2(2pi/9) + cos^2(3pi/9) + cos^2(4pi/9) = 4-9/4 = 7/4}}}<br>
ANSWER: 7/4<br>