Hello from MrBillDoesMath!
Answer:
Choice B, 4
Discussion:
From the Pythagorean Theorem
x^2 + ( x-2)^2 = ( sqrt(20) ) ^ 2 =>
x^2 + ( x^2 - 4x + 4) = 20 => combine common terms
2x^2 -4x + 4 = 20 => divide both sides by 2
x^2 -2x + 2 = 10 => subtract 10 from both sides
x^2 -2x - 8 = 0 => x^2 -2x - 8 = (x-4)(x+2)
(x-4)(x+2) = 0 =>
x = 4, x = -2
The answer is Choice B, 4
Thank you,
MrB