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9x2+21x-5=-15

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1 Answer

Hello, Cheryl --

This problem can be solved either way. If you are comfortable with factoring, that might be the easiest method.

First, add 15 to both sides and set the result equal to 0:

          9x2 + 21x + 10  =  0

Next, try combinations of factors of 9 and 10 that, when FOILed, will yield the given equation. In this case, we come up with:

          (3x + 5)(3x + 2)  =  0

Set each part equal to 0, and solve separately:

         (3x + 5)  = 0      OR    (3x + 2) = 0

                   3x = -5    OR           3x  =  -2

                    x = -5/3    OR      x = -2/3

You will get the same answers using the quadratic formula.