# How do you find side b for a trapezoid?

##### 1 Answer
Oct 18, 2015

$b = \frac{2 A}{h} - a$

#### Explanation:

$A = \frac{h \left(a + b\right)}{2}$ is the formula to find the area of a trapezoid (trapezium), where A is the area, h is the height, a is one parallel side, and b is the other parallel side..

Solving for side $b$ implies that you know the area A, side $a$, and the height.

Multiply both sides times $2$.

$2 A = h \left(a + b\right)$

Divide both sides by $h$.

$\frac{2 A}{h} = a + b$

Subtract $a$ from both sides.

$\frac{2 A}{h} - a = b$

Switch sides.

$b = \frac{2 A}{h} - a$