已知cos α=0.68,求sin α,tan α的值

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已知cos α=0.68,求sin α,tan α的值
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已知cos α=0.68,求sin α,tan α的值
已知cos α=0.68,求sin α,tan α的值

已知cos α=0.68,求sin α,tan α的值
cos α=0.68 = 68/100 = 17/25
sinα = ±√(1-cos^2α) = ±√[1-(17/25)^2] = ±4√21/25
tanα = sinα/cosα = ±4√21/17

sinα=0.57或-0.57
tanα=0.83或-0.83
PS:(sinα)^2+(cosα)^2=1
tanα=sinα/cosα

由sin2a+cos2a=1 (平方相加等于1);所以sin2a=1-cos2a=1-0.682=0.5376
Sina=0.73或sina=-0.73
当a在第一象限角时,sina=0.73 tana=sina/cosa=1.08
当a在第四象限角时,sina=-0.73 tana=sina/cosa=-1.08

(sin α)^2+(cos α)^2=1,所以sin α,tan α有两个值