Question

Помогите пожалуйста, СРОЧНО!!​

Answer 1

$cos(a-b)=cosa*cosb+sina*sinb$

$sina=\sqrt{1-(-0.6)^2}=0.8$

$sinb=\sqrt{1-(\frac{15}{17}^2 )} =\frac{8}{17}$

$cos(a-b)=-0.6*\frac{15}{17} +0.8*\frac{8}{17}=-\frac{13}{85}$