Question

What is the value of x?

Answer 1

its A because 5 squared = 25 and 12 squared = 144 so 144+ 25= 169. 
169=13 squared so its 13 or A

s.a: A

Answer 2

You're trying to find the longest side of a right triangle, also known as the hypotenuse. The formula used is called the Pythagorean Theorem.
a^2+b^2=c^2
5^2+12^2=c^2
25+144=c^2
169=c^2
13=c