Question

What is the value of x

Answer 1

Use pythagorean theorem for the answer.

a^2 +b^2 = c^2

side + side = hypotenuse

Now try to solve it.

Hope that helps:)

Answer 2

The letter "x" is often used in algebra to mean a value that is not yet known. 

It is called a "variable" or sometimes an "unknown".