What is the value of x?

Answer:
x = 3 sqrt 2
Step-by-step explanation:
We know that this is a 45, 45m 90 special right triangle. In this special right triangle the side lengths are x, x and the hypotenuse is x sqrt 2 (we can prove this using pythagoreans theorem). 6 is the hypotenuse, meaning that it is equal to x sqrt 2:
6 = x sqrt 2
x = 6/sqrt 2
Rationalize the denominator:
x = (6 sqrt 2)/2
x = 3 sqrt 2