y=sin(π/4+x/2)sin(π/4-x/2)
=sin(π/4+x/2)sin[π/2-(π/4+x/2)]
=sin(π/4+x/2)cos(π/4+x/2)
=1/2sin(π/2+x)
=1/2cosx
单调递增区间为
[2kπ-π,2kπ],k∈Z