Answer : (-∞,-1) U (-1, 1)
We need to find the interval(s) over which the function is increasing
We look at the intervals of x where the graph is increasing
Increasing interval of the graph is the part where the graph goes up.
At first the graph starts increasing and it increases till x=-1
So the first increasing interval is -infinity to -1 . We write it as (-∞,1)
Now, we look at the part where the graph changes direction
In the middle inverted U shaped graph , the graph starts increasing at x=-1 and increases till it changes direction. The graph is increasing till x=1
so second increasing interval is x=-1 to 1. we write it as (-1,1)
Now combine both intervals by a 'U' union
(-∞,-1) U (-1, 1)
