fx=1+2sin(2x-π/3),x属于[π/4,π/2]
2x-π/3属于[π/6,π2/3]sin(2x-π/3)属于[1/2,1]
fx属于[2,3]
若不等式-2<fx-m<2在[π/4,π/2]上恒成立则1