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

(1+cos50)/2-(1+cos130)/2=1/2+1/2cos50-1/2+1/2cos50=cos50

cos²25°-cos²65°=1. cos²25°=(cos25°)²=(cos(90°-65°))²=(sin65°)²=sin²65°2. sin²65°-cos²65°=-(cos²65°-sin²65°)=-cos(2*65°)=-cos130°3. -cos130°=-cos(180°-50°)=-(-cos50°)=cos50°4. ответ: cos²25°-cos²65°=cos50°