因为sin（x)的单调递增区间为[-π/2+2*k*π，π/2+2*k*π]所以-π/2+2*k*π<=2x+π/4<=π/2+2*k*π得到-3*π/8+k*π<=x<=π/8+k*π所以单调递增区间为-3*π/8<=x<=π/8递减区间就不用我说了吧
