sin²a+sin²75°=1,且a为锐角,则a=_______
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![sin²a+sin²75°=1,且a为锐角,则a=_______](/uploads/image/z/15170189-5-9.jpg?t=sin%26%23178%3Ba%2Bsin%26%23178%3B75%C2%B0%3D1%2C%E4%B8%94a%E4%B8%BA%E9%94%90%E8%A7%92%2C%E5%88%99a%3D_______)
sin²a+sin²75°=1,且a为锐角,则a=_______
sin²a+sin²75°=1,且a为锐角,则a=_______
sin²a+sin²75°=1,且a为锐角,则a=_______
解由sin²a+sin²75°=1
又由cos²75+sin²75°=1
即sin²a=cos²75
即sina=cos75°
即sina=cos(90°-15°)=sin15°
即a=15°.