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证明sin^4α-cos^4α=2sinα²-1
人气:445 ℃ 时间:2020-03-15 12:10:48
解答
左边=(sin²α+cos²α)(sin²α-cos²α)
=sin²α-cos²α
=sin²α-(1-sin²α)
=2sin²α -1
=右边
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