已知tanα=-1/2,则(sinα-cosα)²/cos2α=?

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已知tanα=-1/2,则(sinα-cosα)²/cos2α=?已知tanα=-1/2,则(sinα-cosα)²/cos2α=?已知tanα=-1/2,则(sinα-cosα)

已知tanα=-1/2,则(sinα-cosα)²/cos2α=?
已知tanα=-1/2,则(sinα-cosα)²/cos2α=?

已知tanα=-1/2,则(sinα-cosα)²/cos2α=?
(sinα-cosα)²/cos2α
=(sina²-2sinacosa+cosa²)/(cosa²-sina²)
除cosa²
=(tana²-2tana+1)/(1-tana²)
=(1/4+1+1)/(1-1/4)
=(9/4)/(3/4)
=3