A function is increasing if it "points upwards".
Think that you have two inputs (think of them as being very close to each other). A function
is increasing if
So, smaller input, smaller output.
So:
- In the first segment on the left, the function is decreasing: if you move with little steps rightwards, the output will get smaller and smaller (the function points to the right bottom)
- In the second segment, the line is constant (it's horizontal). This means that even if you consider a larger input, the output reimains the same
- In the third segment, the function is increasing: if you consider a larger input, the output will be larger as well: the function points to the top right.
- In the fourth segment, the function is decreasing again (look at the first bullet point)
So, the function is increasing in the third segment, which is delimited by