Question

Examine the right triangle. What is the length of the hypotenuse, c? Answers are in the pic

Answer 1

a^2+b^2=c^2 <----- the equation to find out sides for a right triangle

Answer 2

Every right triangle follows the pythagorean theorem: given the legs $a$ and $b$ and the hypothenuse $c$ we have

$a^2+b^2=c^2 \implies c=\sqrt{a^2+b^2}$

In your case, a=3 and b=5, so we have

$c=\sqrt{3^2+5^2}=\sqrt{9+25}=\sqrt{34}$