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You try to find factors of 20 that add to 3.

Factors of 20 are 1/20, 2/10 & 4/5. You can't make 3 out of any of these so you have to use the quadratic formula:

x = (-b +/- (sqrt(b squared - 4 ac)))/2a

In your equation a = 1, b = -3 and c = -20

(3 +/- (sqrt(9 + 80)))/2

= (3 +/- sqrt 89)/2

= (3 +/- 9.434)/2

= 12.434/2 and -6.434/2

= 6.217 and -3.217 which are the values for x when your equation equals zero.

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Q: How do you solve x2 -3x -20?
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