If we use the Pythagorean theorem of a^2 + b^2= c^2, we can find x.
a= x
b= 12
c= 13 (the hypotenuse)
a^2 + b^2= c^2
x^2 + (12)^2= (13)^2
remember when squaring, multiply the number by itself one time
x^2 + 144= 169
subtract 144 from both sides
x^2= 25
take the square root of x & 25
x= 5
ANSWER: x= 5
Hope this helps! :)