Question

cos75*cos15 помогите решить

Answer 1

решаем по формуле

$\cos(x) \times \cos(y) = \frac{1}{2}( \cos(x - y) + \cos(x + y))$

cos75*cos15= 1/2(cos(75-15)+cos(75+15))= 1/2(cos60+cos90)= 1/2(1/2+0)=1/4