How do you solve x^2 = 7x +8 using the quadratic formula?

1 Answer
Nghi N.
May 28, 2016

8 and -1

Explanation:

y = x^2 - 7x - 8 = 0
Solving by shortcut. Since a - b + c = 0, then, the 2 real roots are: -1 and -c/a = 8.
Solving by the improved quadratic formula (Google Search)
D = d^2 = b^2 - 4ac = 49 + 32 = 81 --> d = +- 9
There are 2 real roots:
x = -b/(2a) +- d/(2a) = 7/2 +- 9/2 = (7 +- 9)/2
x = 16/2 = 8 and x = -2/2 = -1

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