定义域-1<=x^2-2<=1
1<=x^2<=3
1<=x<=√3或-√3<=x<=-1
y=arccosx是减函数
则当x^2-2单调递减时
y=arccos(x^2-2)的单调递增
在1<=x<=√3或-√3<=x<=-1中
-√3<=x<=-1递减
所以单调递增区间是[-√3,-1]