Quadratic Formula for solving 4x^2-21x-18=0

4x^2-21x-18=0
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a = 4, b = -21, c = -18

to keep from getting "mixed up", evaluate the discriminant first ...

b<sup>2</sup> - 4ac = (-21)<sup>2</sup> - 4(4)(-18) = 729

sqrt(729) = 27

x = (21 +/- 27)/8
x = -3/4, x = 6

since the discriminant is a perfect square, the original quadratic will factor ...

4x<sup>2</sup> - 21x - 18 = 0
(4x + 3)(x - 6) = 0

x = -3/4, x = 6

btw ... why did you post this in the calculus section?
 
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