Помагите с алгерой ,cos2 25°-cos2 65° упрастит надо

Cos25°-cos65°= 1. cos25°=(cos25°)=(cos(90°-65°))=(sin65°)=sin65° 2. sin65°-cos65°=-(cos65°-sin65°)=-cos(2*65°)=-cos130° 3. -cos130°=-cos(180°-50°)=-(-cos50°)=cos50° 4. ответ: cos25°-cos65°=cos50°