The right triangle from the picture is shown below
Looking at the right triangle,
hypotenuse = lonngest side = x
one leg = 12
other leg = 9
We would find x by applying the pythagorean theorem which is expressed as
hypotenuse^2 = one leg^2 + other leg^2
By substituting these values, we have
x^2 = 12^2 + 9^2 = 144 + 81
x^2 = 225
Taking square root of both sides,
[tex]\begin{gathered} x\text{ = }\sqrt[]{225} \\ x\text{ = 15} \end{gathered}[/tex]
x = 15
