Question

Найдите cos(60-a), если sin a=0,6 и 0<a<pi/2

Answer 1

$cos a= \sqrt{1- 0.6^{2} } =0.8$
cos(60-a)=cos60cosa+sin60sina=0.5*0.8+sqrt(3)/2*0.6=0.4+0.3*sqrt(3)