Answer:
Pythagorean theorem
Step-by-step explanation:
You should use the Pythagorean theorem
a^2+b^2 = c^2 where a and b are the legs and c is the hypotenuse
9^2+ 12^2 = ?^2
81 +144 = ?^2
225 = ?^2
Take the square root of each side
sqrt(225) = sqrt(?^2)
15 =?
