#### Answer

Obtuse Triangle

#### Work Step by Step

Using the Pythagorean Theorem...
$a^{2}+b^{2}=c^{2}$
$5^{2}+7^{2}=9^{2}$
Simplify...
$25+49=81$
$74\ne81$
Since the sum of the sides squared $(74)$ is less than the hypotenuse squared $(81)$, the triangle is an obtuse triangle.