SOLUTION: 35y^3-60y^2-20y Factor the trinomial completely

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Question 191479: 35y^3-60y^2-20y
Factor the trinomial completely

Answer by jim_thompson5910(35256)   (Show Source): You can put this solution on YOUR website!

Start with the given expression


Factor out the GCF


Now let's focus on the inner expression




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Looking at we can see that the first term is and the last term is where the coefficients are 7 and -4 respectively.

Now multiply the first coefficient 7 and the last coefficient -4 to get -28. Now what two numbers multiply to -28 and add to the middle coefficient -12? Let's list all of the factors of -28:



Factors of -28:
1,2,4,7,14,28

-1,-2,-4,-7,-14,-28 ...List the negative factors as well. This will allow us to find all possible combinations

These factors pair up and multiply to -28
(1)*(-28)
(2)*(-14)
(4)*(-7)
(-1)*(28)
(-2)*(14)
(-4)*(7)

note: remember, the product of a negative and a positive number is a negative number


Now which of these pairs add to -12? Lets make a table of all of the pairs of factors we multiplied and see which two numbers add to -12

First NumberSecond NumberSum
1-281+(-28)=-27
2-142+(-14)=-12
4-74+(-7)=-3
-128-1+28=27
-214-2+14=12
-47-4+7=3



From this list we can see that 2 and -14 add up to -12 and multiply to -28


Now looking at the expression , replace with (notice adds up to . So it is equivalent to )




Now let's factor by grouping:


Group like terms


Factor out the GCF of out of the first group. Factor out the GCF of out of the second group


Since we have a common term of , we can combine like terms

So factors to


So this also means that factors to (since is equivalent to )



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So our expression goes from and factors further to


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Answer:

So completely factors to

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