21. x^2 + 9x - 14 = 0
x^2 + 9x = 14
x^2 + 9x + (4.5)^2 = 14 + (4.5)^2
(x + 4.5)^2 = 14 + 20.25 = 34.25
x + 4.5 = + or - sqrt(34.25)
x = + or - sqrt(34.25) - 4.5
x = sqrt(34.25) - 4.5 or -sqrt(34.25) - 4.5
x = 5.85 - 4.5 or -5.85 - 4.5
x = 1.35 or -10.35
Answer: the last option.
