Упростить: (cos18° cos7° - sin18°sin7°)² + (sin15° cos10° + cos15° sin10°)²

Question

Упростить:
(cos18° cos7° - sin18°sin7°)² + (sin15° cos10° + cos15° sin10°)²

Answer 1

(cos18° cos7° - sin18°sin7°)² + (sin15° cos10° + cos15° sin10°)² = cos^2(18+7)+sin^2(15+10)=cos^2 25+sin^2 25=1