SOLUTION: Factor the Polynomial:
3x^2-14x-5
I have tried to find the two sets of numbers that will give me the sum of 14 and the product of 15 but I just cant figure it out.
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3x^2-14x-5
I have tried to find the two sets of numbers that will give me the sum of 14 and the product of 15 but I just cant figure it out.
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Question 546776: Factor the Polynomial:
3x^2-14x-5
I have tried to find the two sets of numbers that will give me the sum of 14 and the product of 15 but I just cant figure it out. Found 2 solutions by Edwin McCravy, scott8148:Answer by Edwin McCravy(20056) (Show Source):
3x² - 14x - 5
Your error is that you don't want two numbers that will give you
a SUM of 14 and a product of 15.
Instead you want two numbers that will give you a DIFFERENCE of 14
and a product of 15.
The way you tell whether you want a SUM or a DIFFERENCE is by
looking at the last sign in 3x²-14x-5, which is the sign of -5,
which is NEGATIVE, so that tells you that you want a DIFFERENCE
of 14, not a SUM of 14.
The factors of 15 are
15×1 and the difference is 15-1 which is the 14 you want.
5×3 and the difference is 5-3 which is 2 which you DON'T want.
So use 15 and 1 to rewrite the middle term -14x by giving them
the proper signs. The larger is 15, and it gets the same sign
as the middle term of 3x²-14x-5, which is -, so here goes:
3x²-14x-5
3x² - 15x + 1x - 5
Factor 3 out of the first two terms and +1 out of the last three:
3x(x - 5) + 1(x - 5)
(x - 5)(3x + 1)
I have a tutorial on the AC method of factoring. Go here to see it:
http://www.algebra.com/my/change_this_name32371.lesson?content_action=show_dev
Edwin