解答；
y=3sinx(π/4-2x)=-3sinx(2x-π/4),
(1) 2x-π/4=2kπ+π/2,即 x=kπ+3π/8时,y有最小值-3,此时x的取值集合{x|x=kπ+3π/8,k∈Z};
2x-π/4=2kπ-π/2,即 x=kπ-π/8时,y有最大值3,此时x的取值集合{x|x=kπ-π/8,k∈Z}
(2)y=3sinx(π/4-2x)=-3sinx(2x-π/4),
①减区间,即求y=sinx(2x-π/4)的增区间
2kπ-π/2 ≤ 2x-π/4 ≤ 2kπ+π/2
2kπ-π/4 ≤ 2x ≤ 2kπ+3π/4
kπ-π/8 ≤ x ≤ kπ+3π/8
所以,y=3sin(π/4-2x)的单调减区间[kπ-π/8 , kπ+3π/8],k∈Z
②增区间,即求y=sinx(2x-π/4)的减区间
2kπ+π/2 ≤2x- π/4 ≤ 2kπ+3π/2
2kπ+3π/4 ≤ 2x ≤ 2kπ+7π/4
kπ+3π/8 ≤ x ≤ kπ+7π/8
所以,y=3sin(π/4-2x)的单调增区间[kπ+3π/8 , kπ+7π/8],k∈Z