A square has an area of 12x^2 square feet. What is the length of its sides?

The area of a rectangle is found by multiplying the length by the width or L*W.
In a square the length and width are the same so just call the value
s for each side.

l*w = s*s = s2

In this case we have
s2 = 12x2 Take square root of both sides
s = √(12x2)
s = x√12
s = x√(4*3)
s = x√(22*3)
s = 2x√3

If you want the variable at the end of the number
you can write this as (2√3)x
I only put the parentheses to denote that the
term x is not part of the square root.