This is the start of our APPLICATIONS of integrals section! Here you will be looking at two different areas a function can create with the x-axis and adding them up.
Note: In previous chapters you may have seen area like:

which would have cancelled out and = 0. HOWEVER, with signed area, we take the absolute value of the (-) area so that we can add these together.
The definite integral signed area (cr: Joel Speranza Math)