已知cos(x-派/4)=根号2/10,x属于(派/2,3派/4)求sinx的值
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![已知cos(x-派/4)=根号2/10,x属于(派/2,3派/4)求sinx的值](/uploads/image/z/572390-62-0.jpg?t=%E5%B7%B2%E7%9F%A5cos%28x-%E6%B4%BE%2F4%29%3D%E6%A0%B9%E5%8F%B72%2F10%2Cx%E5%B1%9E%E4%BA%8E%28%E6%B4%BE%2F2%2C3%E6%B4%BE%2F4%29%E6%B1%82sinx%E7%9A%84%E5%80%BC)
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已知cos(x-派/4)=根号2/10,x属于(派/2,3派/4)求sinx的值
已知cos(x-派/4)=根号2/10,x属于(派/2,3派/4)求sinx的值
已知cos(x-派/4)=根号2/10,x属于(派/2,3派/4)求sinx的值
cos2(x-派/4)=2cos(x-派/4)^2-1=-24/25=cos(2x-π/2)=-sin2x
所以 sin2x=24/25=2sinx*cosx cos2x=-7/25 =1-2sinx^2
sinx>0 得sinx=4/5
sinX=4/5