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

1 Answer
Nghi N.
Apr 9, 2016

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

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