Solve for x over the real numbers:
x^2 - 15 = -4 x
Add 4 x to both sides:
x^2 + 4 x - 15 = 0
Add 15 to both sides:
x^2 + 4 x = 15
Add 4 to both sides:
x^2 + 4 x + 4 = 19
Write the left hand side as a square:
(x + 2)^2 = 19
Take the square root of both sides:
x + 2 = sqrt(19) or x + 2 = -sqrt(19)
Subtract 2 from both sides:
x = sqrt(19) - 2 or x + 2 = -sqrt(19)
Subtract 2 from both sides:
Answer: x = sqrt(19) - 2 or x = -2 - sqrt(19)