Question

Спростити: cos×2 15-sin×2 15=​

Answer 1

cos^2 15- sin^2 15= cos 30

Answer 2

$\cos {}^{2} (15) - \sin {}^{2} (15) = \cos {}^{2} (15) - (1 - \cos {}^{2} (15) ) = 2 \cos {}^{2} (15) - 1 = \cos(2 \times 15) = \cos(30) = \frac{ \sqrt{3} }{2}$