x∈[0,π]那么π/4<=2x+π/4<=9π/4所以最大值为3*1=3，最小值=3*(-1)=-3设t=2x+π/4当π/4<=t<=9π/4y=3sint增区间为[π/4,π/2]与[3π/2,9π/4]对应x的递增区间为[0,π/8]与[5π/8，π]x的递减区间为[π/8，5π/8]
