Solve for x:
x^2+4 x+21 = 0
Subtract 21 from both sides:
x^2+4 x = -21
Add 4 to both sides:
x^2+4 x+4 = -17
Write the left hand side as a square:
(x+2)^2 = -17
Take the square root of both sides:
x+2 = i sqrt(17) or x+2 = -i sqrt(17)
Subtract 2 from both sides:
x = i sqrt(17)-2 or x+2 = -i sqrt(17)
Subtract 2 from both sides:
Answer: | x = i sqrt(17)-2 or x = -i sqrt(17)-2
