求sin²20°+sin80°sin40°,并且要用sin(α+β)sin(α-β)=sin²α-sin²β公式运算不要复制别人的!
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![求sin²20°+sin80°sin40°,并且要用sin(α+β)sin(α-β)=sin²α-sin²β公式运算不要复制别人的!](/uploads/image/z/565440-24-0.jpg?t=%E6%B1%82sin%26%23178%3B20%C2%B0%2Bsin80%C2%B0sin40%C2%B0%2C%E5%B9%B6%E4%B8%94%E8%A6%81%E7%94%A8sin%28%CE%B1%2B%CE%B2%29sin%28%CE%B1-%CE%B2%29%3Dsin%26%23178%3B%CE%B1-sin%26%23178%3B%CE%B2%E5%85%AC%E5%BC%8F%E8%BF%90%E7%AE%97%E4%B8%8D%E8%A6%81%E5%A4%8D%E5%88%B6%E5%88%AB%E4%BA%BA%E7%9A%84%21)
求sin²20°+sin80°sin40°,并且要用sin(α+β)sin(α-β)=sin²α-sin²β公式运算不要复制别人的!
求sin²20°+sin80°sin40°,并且要用sin(α+β)sin(α-β)=sin²α-sin²β公式运算
不要复制别人的!
求sin²20°+sin80°sin40°,并且要用sin(α+β)sin(α-β)=sin²α-sin²β公式运算不要复制别人的!
sin²20°+sin80°sin40°
=sin²20°+sin^2(60°)-sin²20°
=3/4