已知cos(π/4+x)=3/5,17π/12＜x＜7π/4,求sin2x+2sin平方x/（1-tanx）的值
问题描述：
已知cos(π/4+x)=3/5,17π/12＜x＜7π/4,求sin2x+2sin平方x/（1-tanx）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•...