Question

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

Answer 1

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

Answer 2

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°