Question

Найдите сумму
$sin^{4}15+cos^{4}15$

Answer 1

$\sin^415а+\cos^415а=\sin^415а+\cos^415а\pm2\sin^215а\cos^215а=\\ =(\sin^215а+\cos^215а)^2-2\sin^215а\cos^215а=1^2- \frac{\sin^230а}{2} =0.875$