12 cm
5 cm
what’s the hypotenuse

13 cm

explanation:
pythagorean theorem to find the hypotenuse ( which is c)
a^2 + b^2 = c^2
let’s just say a=5 and b = 12
5^2 + 12^2 = c^2
25 + 144 = c^2
169 = c^2 -> take the square root of both sides
√169 = √c^2
c = 13

OR you can memorize a few pythagorean triples and know 13 is the hypotenuse bc 5-12-13 is a pythagorean triple so 13 is the hypotenuse