## Precalculus (10th Edition)

$19.81$ square units
Using Heron's formula, the area $A$ of a triangle is $A=\sqrt{s(s-a)(s-b)(s-c)}$, where $s=\frac{a+b+c}{2}.$ Hence, here we have $s=\frac{5+8+10}{2}=11.5$, Thus, $A=\sqrt{11.5(11.5-5)(11.5-8)(11.5-10)}\approx19.81$