The area formula and the coordinate plane

The area of a rectangle is its length times its width: A = l × w. It works for any numbers, whole or fractions. A square is a rectangle whose sides are equal, so A = s × s. Area is measured in square units: square centimetres, square metres. If you know the area and one side, divide to find the other side: w = A ÷ l, because multiplying and dividing undo each other. For a shape made of rectangles, such as an L-shape, there are two ways. Way 1: cut it into rectangles, find each area and add. Way 2: imagine a bigger rectangle, find its area and subtract the missing corner. Both ways must give the same area, so one way can check the other.