漏了平方了
1-2sin²（x+8分之π）+2sin（x+8分之π）cos（x+8分之π）
原式=cos[2(x+π/8)]+sin[2(x+π/8)]
=sin(2x+π/4)+cos(2x+π/4)
=√2[sin(2x+π/4)*√2/2+cos(2x+π/4)*√2/2]
=√2[sin(2x+π/4)cosπ/4+cos(2x+π/4)sinπ/4]
=√2sin(2x+π/4+π/4)
=√2sin(2x+π/2)
=√2cos2x
所以T=2π/2=π
cosx增区间(2kπ-π,2kπ)
减区间(2kπ,2kπ+π)
则这里增区间2kπ-π