Question

example 16: the lengths of two sides of a triangular window are 7 feet and 5 feet. the perimeter is 18 feet. how long is the third side?

Explanation:

Step1: Recall perimeter formula

Let the third - side length be $x$. Perimeter $P=a + b+x$, where $a = 7$, $b = 5$ and $P = 18$.

Step2: Substitute values and solve

$18=7 + 5+x$, so $18=12+x$. Then $x=18 - 12$.

Answer:

6 feet