Answer : (0,3) U (3, ∞)
We need to find the interval(s) over which the function is decreasing
We look at the intervals of x where the graph is decreasing
Decreasing interval of the graph is the part where the graph goes down
We look at the part where the graph changes direction
In the middle inverted U shaped graph , the graph changes direction and start decreasing at x=0
the graph is decreasing till x=3
so first decreasing interval is x=0 to 3. we write it as (0,3)
After x=3 the graph starts decreasing and it goes to infinity
So the second decreasing interval is 3 to infinity . We write it as (3, ∞)
Now combine both intervals by a 'U' union
(0,3) U (3, ∞)
