Question

How do you solve `x^2 + 5x + 1 = 0` using the quadratic formula?

Answer 1

`(-5 +- sqrt21)/2`

Explanation:

Use the improved quadratic formula (Google, Yahoo Search).
`D = d^2 = b^2 - 4ac = 25 - 4 = 21` --> `d = +- sqrt21`
There are 2 real roots:
`x = -b/(2a) +- d/(2a) = -5/2 +- sqrt21/2 = (-5 +- sqrt21)/2`