不查表求下列各式的值谢谢啦 1.cos²75°-s - 知识问答

不查表求下列各式的值谢谢啦 1.cos²75°-sin²75° 2.cos80°*cos35°+cos10°*cos55

1个回答

1.cos²75°-sin²75°
=cos(2×75°)
=cos150°
=-cos30°
=-(√3)/2
2.cos80°*cos35°+cos10°*cos55°
=cos(80°-35°)
=cos45°
=(√2)/2
3.sin14°*cos16°+sin76°*cos74°
=sin14°*cos16°+cos14°*sin16°
=sin(14°+16°)
=sin30°
=1/2

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