若cos(π/4-x)=-4/55π/4＜x＜7π/4求(sin2x-2sin^2x)/1+tanx的值求值已知π/2

Question

若cos(π/4-x)=-4/5 5π/4＜x＜7π/4 求 (sin2x-2sin^2x)/1+tanx 的值
求值已知π/2

Answer 1

cos(π/4-x)=-4/5得(√2/2)(cosx+sinx）=-4/5
所以cosx+sinx=-4√2/5 -----------（1）
cos(π/4+x)=sin(π/2-π/4-x)=sin(π/4-x)=-3/5(因为5π/4