#### Answer

The student incorrectly substituted the given length of the hypotenuse (13) into the equation where the length of a leg should have been used.
x=5

#### Work Step by Step

In the equation a2+b2=c2, a and b are the lengths of the two legs and c is the length of the hypotenuse.
$a^2+b^2=c^2$⟶ substitute the given values
$122+x^2=133$⟶ compute the squares
$144+x^2=169$⟶ subtract 144 from each side
$144+x^2−144=169−144$⟶ subtract
$x^2=25$⟶ find the square root of each side
$x=5$