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问题: 复合函数的单调性

求y=log1/2[sin(派/3-x派/4)]的单调减区间。

解答:

求y=log1/2[sin(派/3-x派/4)]的单调减区间;

y = log_(1/2)(g(x)),
当 g(x) 增加,y减少; g(x)减少,y增加;

sin(PI/3-x*PI/4)
2kPI-PI/2 <=PI/3-x*PI/4<=2kPI+PI/2
-8k-2/3 <=x<=-8k+10/3
sin(PI/3-x*PI/4)单独递增,y 单调减;

y=log1/2[sin(派/3-x派/4)]的单调减区间是
-8k-2/3 <=x<=-8k+10/3,
[-8k-2/3, -8k+10/3], k是整数.