已知cos(四分之π+x)=五分之三,求1-tanx分之sin2x-2sin^2x的值
问题描述:
已知cos(四分之π+x)=五分之三,求1-tanx分之sin2x-2sin^2x的值
答
17π/12<x<7π/4,得5π/3<x+π/4<2π cos(x-π/4)=cos[(x+π/4)-π/2]=sin(x+π/4)=-√[1-sin²(x+π/4)]=-√[1-(3/5)²]=-4/5 sin(2x)=-cos(2x+π/2)=-cos[2(x+π/4)]=1-2cos²(x+π/4)=1-2•...