sina-cosa=1/2,求sin^3a-cos^3a值
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sina-cosa=1/2,求sin^3a-cos^3a值
sina-cosa=1/2,求sin^3a-cos^3a值
sina-cosa=1/2,求sin^3a-cos^3a值
由sina-cosa=1/2等式两边平方有
(sina-cosa)^2=sin^2a+cos^2a+2sinacosa=1-2sinacosa=1/4
即sinacosa=3/8
又sin^3a-cos^3a=(sina-cosa)(sin^2a+sinacosa+cos^2a)=1/2 * (1+3/8)=11/16
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