Will give brainliest to correct answer.

It's going to be kind of crazy, but you need to use Pythagorean's Theorem for this.  That will look like this: .  FOIL out the left side to get .  FOIL out the first of the 2 expressions on the right to get ,  and the second of the 2 to get 4x.  Our equation now looks like this:  .  Combine like terms to get an equation that still has square roots in it that we have to deal with:    and .  We will square both sides to get rid of the square root sign.  .  This is a polynomial now that can be factored to solve for x.  Bring the 2x over by subtraction and set the polynomial equal to 0.  .  Factor out an x, leaving us with  x(x-2)=0.  That means that x = 0 or x - 2 = 0 and x = 2.  Of course if we are solving for the length of a side we know it can't have a side length of 0, so it must have a side length that is a multiple of 2.  x = 2