1.已知cos(π/4+x)=3/5,255°<x<315°,求(sin2x+2sin²x)/(1-tanx)的值

问题描述:

1.已知cos(π/4+x)=3/5,255°<x<315°,求(sin2x+2sin²x)/(1-tanx)的值

cos(π/4+x)=3/5,3/2π<π/4+x<2π,所以sin(π/4+x)=-4/5,Sin2x=-cos(π/2+2x)=-cos[2(π/4+x)]=-[1-2sin²(π/4+x)]=7/25.sinx+cosx=√2* sin(π/4+x)=-4√2/5,cosx –sinx=√2* cos(π/4+x)=3√2/5,(sin...