直线L的倾斜角为α,且满足sinα+cosα=负1/5，求直线l的斜率

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sina+cosa=-1/5
sin^a+cos^a=1
联立上掘渗二方程解得判棚脊sina=3/5
cosa=-4/5
l的斜率=tana=sina/cosa=-3/和源4

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sinα+cosα=-1/5与（sinα）谨乱^2+（cosα）^2=1联立孝嫌得sinα=3/5 cosα=-4/5，tanα=sinα/cosα=-3/4
即斜巧晌手率为-3/4

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