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How do I solve for x using quadratic formula x^2+x-18=0

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smallsterea | (Level 1) Honors

Posted June 12, 2013 at 11:00 PM via web

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How do I solve for x using quadratic formula

x^2+x-18=0

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llltkl | College Teacher | (Level 3) Valedictorian

Posted June 13, 2013 at 12:38 AM (Answer #1)

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The solutions (for x) of a quadratic equation of the form:

 `ax^2 + bx + c = 0`

can be elegantly found using the quadratic formula. The solutions are: `x = (-b+-sqrt(b^2-4*a*c))/(2*a)`

The given quadratic equation is: `x^2 + x - 18 = 0`

here, a =1, b = 1 and c = -18

Putting the values in the quadratic formula yields

`x = (-1+-sqrt(1^2-4*1*(-18)))/(2*1)`

= `(-1+-sqrt(1+72))/2`

= `(-1+-sqrt(73))/2`

= `(-1+8.544)/2` and `(-1-8.544)/2`

= `3.772` and `-5.772` (approximately).

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