SOLUTION: Ok, I'm working on factoring completely. Here is my equation to factor: -4n^4 + 40n^3 - 100n^2 that equals = -4n^2 (n^2 - 10n + 25) and I'm supposed to factor it d

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Question 405542: Ok, I'm working on factoring completely.
Here is my equation to factor:
-4n^4 + 40n^3 - 100n^2
that equals =
-4n^2 (n^2 - 10n + 25)
and I'm supposed to factor it down more so that the answer is
-4n^2(n - 5)^2
I get it all until the last step. How and Why am I supposed to do that?
Mucho thanks for any help!

Found 2 solutions by ewatrrr, jim_thompson5910:
Answer by ewatrrr(24785)   (Show Source): You can put this solution on YOUR website!

Hi
-4n^4 + 40n^3 - 100n^2
-4n^2 (n^2 - 10n + 25) |good work with this
-4n^2 (n-5)(n-5) |to complete, the quadratic expression can be factored
Note:SUM of the inner product(-5n) and the outer product(-5n) = -10n
Finaly, can be written
-4n^2 (n-5)^2
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




------------------------------------------------------------



Looking at we can see that the first term is and the last term is where the coefficients are 1 and 25 respectively.

Now multiply the first coefficient 1 and the last coefficient 25 to get 25. Now what two numbers multiply to 25 and add to the middle coefficient -10? Let's list all of the factors of 25:



Factors of 25:
1,5

-1,-5 ...List the negative factors as well. This will allow us to find all possible combinations

These factors pair up and multiply to 25
1*25
5*5
(-1)*(-25)
(-5)*(-5)

note: remember two negative numbers multiplied together make a positive number


Now which of these pairs add to -10? Lets make a table of all of the pairs of factors we multiplied and see which two numbers add to -10

First NumberSecond NumberSum
1251+25=26
555+5=10
-1-25-1+(-25)=-26
-5-5-5+(-5)=-10



From this list we can see that -5 and -5 add up to -10 and multiply to 25


Now looking at the expression , replace with (notice combines back 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 )


note: is equivalent to since the term occurs twice. So also factors to



------------------------------------------------------------




So our expression goes from and factors further to


------------------
Answer:

So factors to

If you need more help, email me at jim_thompson5910@hotmail.com

Also, please consider visiting my website: http://www.freewebs.com/jimthompson5910/home.html and making a donation. Thank you

Jim

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