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Instant Math
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–3x2 + 5x + 12 = 0
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Jasman004

by Jasman004 at December 07, 2009

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When I'm trying to factor a trinomial like this, I like to list the factors of the first and last terms: 1, 3 (and one of them has to be negative)1, 12, 3, 4, 2, 6Then I see what combinations might get me to the middle term. In this case, I see that multiplying 3 by 3 and -1 by 4 would get me 9x and -4x, which adds up to the middle term 5x. So my solution is:(3x + 4)(-x + 3)Hope that helps.
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Larry084 Larry084 December 07, 2009

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using factoring by grouping (which i find better that trial and error) you find the product of a and c (which in this case are 3 and 12).  The product is 36.  b is 5.  so then you find 2 numbers whose product is 36 and sum is 5. 2 such numbers are 9 and -4.  So you rewrite the equation as 3x^2 + 9x - 4x + 12=0 (which is equivalent to the first equation.  Then you factor out the commons in the first 2 terms and the last 2 terms and end up with 3x(-x+3) + 4(-x+3).  Then you factor out the commons of that and get (-x +3)(3x + 4). If you foil, you end up with what you started with. 
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DoggiLov DoggiLov December 08, 2009

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