Cos125градусов*cos5градусов + sin55градусов*cos85градусов

Question

Cos125градусов*cos5градусов + sin55градусов*cos85градусов

Answer 1

Cos(90+35)*cos5+sin(90-35)*cos(90-5)=-sin35*cos5+cos35*sin5=
=sin(5-35)=-sin20