Answer:
{-2, 7}
Explanation:
Square both sides of this equation. We get:
18 + x = x^2 - 4x + 4, which, in turn, simplifies to
x^2 - 5x - 14 = 0.
Note that 2 - 7 = -5 and that 2(-7) = -14.
Then x^2 - 5x - 14 = 0 => (x -7)(x + 2) = 0, which gives us the solutions -2 and 7.