# How do you use Heron's formula to find the area of a triangle with sides of lengths 9 , 4 , and 9 ?

$A r e a = \sqrt{p \left(p - a\right) \left(p - b\right) \left(p - c\right)}$
where p is half the perimeter, or $p = \frac{1}{2} \cdot \left(a + b + c\right)$
Now replace values of $a = 9 , b = 4 , c = 9$ to find that
$A r e a \approx 17.55$