The rectangle has opposite sides of equal length. The sides are perpendicular to each other. A square is a special case of a rectangle. Its pages are all the same length.[br] [br]The area of the rectangle is calculated by the formula[br] [br][math]\large\textcolor{blue}{A = \text{base }\cdot\text{height} =ah}[/math][br] [br]In practice, the lengths of adjacent pages are multiplied by each other. The rectangle circuit is the sum of the lengths of all sides. Since the opposite sides are always the same length, the perimeter is easily obtained.[br] [br][math]\large \textcolor{blue}{\text{Perimeter = }2a\cdot 2h}[/math][br][br]

In the parallelogram opposite sides are equal in length and at the same angle. The area of the plane is calculated using the same formula as that of the rectangle. You will see the reason when you pull the slider [i]b[/i] to the right.

In a trapezoid, only two sides are parallel. They don't have to be as long either. The area of the trapezoid is obtained by adding the parallel sides together and the result[br]Divide by two. The number obtained is then multiplied by the perpendicular height. As a formula, it looks like this:[br] [br][math]\large A =\frac{a+b}{2}\cdot h.[/math][br] [br]In the applet above, you can see the figures in their correct places in the formula. You can change the shape of the trapezoid with a slider.