式子cos²（四分之π-α）+cos²（四分之π+α）=
问题描述：
式子cos²（四分之π-α）+cos²（四分之π+α）=
答
cos（π/4-α）=sin[π/2-(π/4-α)]=sin(π/4+α)
所以 cos²（π/4-α）+cos²（π/4+α）=sin²（π/4+α）+cos²（π/4+α）=1sin[π/2-(π/4-α)]=sin(π/4+α)这一步是如何得的？sinπ/2的不是应该得cos吗？这样不就又变回去了吗sin[π/2-(π/4-α)]=sin(π/4+α)这是步是计算，π/2-(π/4-α)=π/2- π/4+ α=π/4+α