Question 316984: Factor:
3x^2-10xy+8y^2
Answer by jim_thompson5910(35256)   (Show Source):
You can put this solution on YOUR website!
Looking at  we can see that the first term is  and the last term is  where the coefficients are 3 and 8 respectively.
Now multiply the first coefficient 3 and the last coefficient 8 to get 24. Now what two numbers multiply to 24 and add to the middle coefficient -10? Let's list all of the factors of 24:
Factors of 24:
1,2,3,4,6,8,12,24
-1,-2,-3,-4,-6,-8,-12,-24 ...List the negative factors as well. This will allow us to find all possible combinations
These factors pair up and multiply to 24
1*24
2*12
3*8
4*6
(-1)*(-24)
(-2)*(-12)
(-3)*(-8)
(-4)*(-6)
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 Number | Second Number | Sum | | 1 | 24 | 1+24=25 | | 2 | 12 | 2+12=14 | | 3 | 8 | 3+8=11 | | 4 | 6 | 4+6=10 | | -1 | -24 | -1+(-24)=-25 | | -2 | -12 | -2+(-12)=-14 | | -3 | -8 | -3+(-8)=-11 | | -4 | -6 | -4+(-6)=-10 |
From this list we can see that -4 and -6 add up to -10 and multiply to 24
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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Answer:
So factors to
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