Cos44*cos16-cos59*cos31=1/4 решите ) незнаю просто как сделать)

cos44*cos16-cos59*cos31=1/4

(1/2)*cos(44-16)+(1/2)*cos(44+16)-(1/2)*cos(59-31)-(1/2)*cos(59+31)=1/4

(1/2)*cos28-(1/2)*cos28+(1/2)*cos60-(1/2)*cos90=1/4

1/4-0=1/4

1/4=1/4

Тождество доказано