So we want three rectangles, each of width units, starting at , ending at ; total width
The mid-point of the first rectangle, then, is at . So this is the first value of to plug into the function; i.e.This is the height of the first rectangle, then. Its area is therefore .
The next value of is at the mid-point of the second rectangle; i.e. at ; and the final value will be at .
Work out and , and then the total area.
I make the answer . Do you?