This type of equation is known as an ax^2 + bx + c.
There is more than one way to go about solving this problem. One way is to try out different possibilities and check by expansion:
We look first at the two possible first terms. They will, in this case, HAVE to be (2x + ___)(x + ____) because 2x * x is the only thing that will give 2x^2.
So then it's a matter of filling those blanks with numbers who have a product of -3, that c in the equation. Fortunately, there aren't a lot of options: -1 and 3, 1 and -3, 3 and -1, -3 and 1. You can use mental math or actually expand the whole thing to discover that it would be -1 and 3:
(2x - 1)(x+3)
Expanded, that would give us 2x^2 + 6x - x - 3 which, simplified, is 2x^2 +5x - 3.
Another way to do this is this:
You figure out the two numbers whose product is a*c and whose sum is 5. a*c in this case is 2 * -3, or -6. If your mental math is good, you'll see right away that you need 6 and -1. We are actually going to use these as 6x and -x to replace the +5x and rewrite the question:
2x^2 + 6x - x - 3
Now I'm going to group the question a bit:
(2x^2 + 6x) + (-x - 3)
I'm now going to pull out any common factors:
2x(x + 3) + -(x + 3), keeping in mind that I've actually pulled out -1 from that second set of brackets.
See how both the part before the + has (x+3) and so does the part after the + ? That is a common factor for both terms. If we pull that out, we're left with:
(x+3)(2x-1)
This second way makes a lot of sense if you've already had practice grouping and factoring after the grouping.
There is also a box method. You can read more about that here: http://www.purplemath.com/modules/factquad2.htm
2007-03-23 13:43:20
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answer #1
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answered by glurpy 7
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when factoring, if the problem has x^2 you know that there is an x in the parentheses. so you would have (2x...)(x...). now you should look at the number if there is one, in this case the number is -3, so that means that one of the values in the parentheses is negative. the combinations are either, (2x+3)(x-1) or (2x-1)(x+3). The factored form of the problem would be (2x-1)(x+3) because if you distribute the numbers you get 2x^2 +6x -1x-3, which is the same as 2x^2+5x-3.
2007-03-23 20:37:44
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answer #2
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answered by summertime 3
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(x+3)(2x-1)
x=-3 , 1/2
2007-03-23 20:30:29
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answer #3
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answered by Dave aka Spider Monkey 7
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(2x-1)(x+3)=0
2007-03-23 20:31:14
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answer #4
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answered by Regrettably Yours, 1
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(2x-1 )(x+3)
2007-03-23 21:09:30
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answer #5
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answered by lifeisgood20 2
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