比如y=2sin(六分之pai减2x) X∈[0,pai]为增函数的区间.

x∈【0,π】π/6-2x∈［-11π/6,π/6］    sinx在［-π3/2,-π/2］上是减函数,所以π/6-2x＝-π3/2　　x=5π/6
π/6-2x=-π/2    x=π/3      增函数的区间{π/3,5π/6]
0<x<π,
0<2x<2π
-π/6<2x-π/6<11π/6
y=2sin(π/6-2x)=-2sin(2x-π/6)
y增函数的区间是sin(2x-π/6)的减区间
π/2<2x-π/6<3π/2
π/3<x<5π/6

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