Question

How do you solve `x^2 - 2x - 15 = 0` using the quadratic formula?

Answer 1

6 and - 2

Explanation:

`y = x^2 - 2x - 15 = 0`
Use the new quadratic formula in intercept form (Google, Yahoo)
`D = d^2 = b^2 - 4ac = 4 + 60 = 64` --> `d = +- 8`
There are 2 real roots:
`x = - b/(2a) +- d/(2a) = 4/2 +- 8/2 = 2 +- 4`

`x1 = 2 + 4 = 6` and `x2 = 2 - 4 = - 2`