Step-by-step explanation:
The image is attached below.
Given AB = 9
BC = x
AC = y = 18
Note that the given triangle is a right angled triangle.
We know that Pythagoras theorem states that in a right angle hypotenuse is equal to the sum of the squares of other two sides.
Using Pythagoras thereom,
Taking square root on both sides,
Hence, the value of x is .