(cos^2 10°-cos^2 80°)+sin^2 20°
问题描述:
(cos^2 10°-cos^2 80°)+sin^2 20°
答
(cos^2 10°-cos^2 80°)²+sin^2 20°
=(cos^2 10°-sin^2 10°)²+sin^2 20°
=cos²20+sin²20°
=1