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在长方形中,设一条对角线与其一顶点出发的两条边所成的角分别是α,β,则有cos2...
在长方形中,设一条对角线与其一顶点出发的两条边所成的角分别是α,β,则有cos2α+cos2β= .类比到空间,在长方体中,一条对角线与从某一顶点出发的三条棱所成的角分别是α,β,γ则有正确的式子是 .
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