# How do you use Heron's formula to find the area of a triangle with sides of lengths 3 , 5 , and 7 ?

Apr 17, 2016

First, I like to start by writing out the formula:
A = $\sqrt{s \cdot \left(s - 1\right) \left(s - b\right) \left(s - c\right)}$, where s = semiperimeter, and a, b, and c are the sides of the triangle.

#### Explanation:

First, perimeter: 3 + 5 + 7 = 15
Then, semiperimeter: $\frac{15}{2}$ or 7.5

Now, Area = $\sqrt{7.5 \left(7.5 - 3\right) \left(7.5 - 5\right) \left(7.5 - 7\right)}$