f(x)=2sin[（π/4)-x]把[（π/4)-x]看成一个整体,
sinx 的单调增区间是（2kπ -π/2,2kπ + π/2)
2kπ -π/2≤（π/4)-x≤2kπ + π/2,解得x范围：（2kπ -π/4,2kπ + 3π/4)
sinx 的单调减区间是（2kπ +π/2,2kπ + 3π/2)
2kπ +π/2≤（π/4)-x≤2kπ + 3π/2,解得x范围：（2kπ +3π/4,2kπ + 7π/4)
f(x)=2sin[（π/4)-x]的单调区间
f(x)=2sin[（π/4)-x]把[（π/4)-x]看成一个整体,
sinx 的单调增区间是（2kπ -π/2,2kπ + π/2)
2kπ -π/2≤（π/4)-x≤2kπ + π/2,解得x范围：（2kπ -π/4,2kπ + 3π/4)
sinx 的单调减区间是（2kπ +π/2,2kπ + 3π/2)
2kπ +π/2≤（π/4)-x≤2kπ + 3π/2,解得x范围：（2kπ +3π/4,2kπ + 7π/4)