## Precalculus (6th Edition) Blitzer

The area of a triangle is approximately $16$ square yards.
The area of a triangle is calculated using Heron's formula where $s$ is equal to half the perimeter of the triangle. The area of the triangle is given by \begin{align} & A=\sqrt{s\left( s-a \right)\left( s-b \right)\left( s-c \right)} \\ & \\ \end{align} where \begin{align} & s=\frac{1}{2}\left( a+b+c \right) \\ & s=\frac{1}{2}\left( 13+9+5 \right)=13.5 \\ \end{align} By substituting the values of s and a, b, c we get, \begin{align} & A=\sqrt{13.5\left( 13.5-13 \right)\left( 13.5-9 \right)\left( 13.5-5 \right)} \\ & A=\sqrt{258.1875}\simeq 16 \\ \end{align}