#### Answer

(3, 4, 5) is a Pythagorean Triple. γ lies opposite the
longest side and must be a right angle.

#### Work Step by Step

To measure the value of r,
We need to use the law of cosines
Since the sides of the triangle is given. They are Pythagorean triplet
$c^{2}$ = $a^{2}$ +$b^{2}$
$5^{2}$ = $3^{2}$ +$4^{2}$
25 = 9 + 16
25 = 25