Вычеслить cos (6 пи/5)sin (3 пи/10)-sin (6пи/5)sin(-4пи/5)

Question

Вычеслить cos (6 пи/5)sin (3 пи/10)-sin (6пи/5)sin(-4пи/5)

Answer 1

Cos6π/5*sin3π/10-sin6π/5*sin(-4π/5)=cos(π+π/5)sin(π/2-π/5)-sin(π+π/5)sin(π+π/5)=
=-cosπ/5cosπ/5-sinπ/5sinπ/5=-(cos²π/5+sin²π/5)=-1

Comments

Спасибо большое)