Find the Area Between Curves:
For this the values are ALWAYS positive, no matter if it goes under the X-axis, this is just the amount of space there.
Abs(Area) in a way.
f(x) represents the “top” function and g(x) represents the “bottom” function.

It doesn’t matter if the function is partially under the x-axis, don’t worry about it being up or down C:

Horizontal Strips Method:
Sometimes there isn’t a clear top and bottom, but then you can integrate along the y-axis.
Where f(y) is the right-most function and g(y) is the left-most function.

The area of Polar curves and between them:
It is the area between two angles, alfa, and beta, which can be a little tricky to find.
You really need to graph them out to see where an angle is.
Below is the equation for the area, and to get between two curves, simply subtract them from two different curves.