Answer:
The expression which is used to find the length of the side x in the right triangle is:

Explanation:
We know that in a right angled triangle the Pythagorean Theorem holds true.
Pythagorean Theorem--
It states that if c is the hypotenuse of the right angled triangle and a and b are two legs of the triangle then the following relation holds true:

Here we have:

Hence, we get by the Pythagorean Theorem that:

But since length can't be negative hence we have:
