Polygons areas formulas

We present the formula to calculate the areas of various geometric shapes, with graphical explanations.

shape	representation	Area
square		$a^2$
rectangle		$a\times b$
right triangle		$\displaystyle\frac{a\times b}{2}$	Check the explanations
triangle		$\displaystyle\frac{a\times b}{2}$	Check the explanations
parallelogram		$a\times b$	Check the explanations
trapezoid		$\displaystyle b\times\frac{a+c}{2}$	Check the explanations