SOLUTION: 70s^2-165sr+90r^2 factor trinomial completely answer I had was 5 5(2a-3(7a-6r) but my answer was wrong please help Thank you

Question 642394: 70s^2-165sr+90r^2 factor trinomial completely
answer I had was 5
5(2a-3(7a-6r) but my answer was wrong please help
Thank you
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 try to factor the inner expression

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

Looking at the expression , we can see that the first coefficient is , the second coefficient is , and the last coefficient is .

Now multiply the first coefficient by the last coefficient to get .

Now the question is: what two whole numbers multiply to (the previous product) and add to the second coefficient ?

To find these two numbers, we need to list all of the factors of (the previous product).

Factors of :
1,2,3,4,6,7,9,12,14,18,21,28,36,42,63,84,126,252
-1,-2,-3,-4,-6,-7,-9,-12,-14,-18,-21,-28,-36,-42,-63,-84,-126,-252

Note: list the negative of each factor. This will allow us to find all possible combinations.

These factors pair up and multiply to .
1*252 = 252
2*126 = 252
3*84 = 252
4*63 = 252
6*42 = 252
7*36 = 252
9*28 = 252
12*21 = 252
14*18 = 252
(-1)*(-252) = 252
(-2)*(-126) = 252
(-3)*(-84) = 252
(-4)*(-63) = 252
(-6)*(-42) = 252
(-7)*(-36) = 252
(-9)*(-28) = 252
(-12)*(-21) = 252
(-14)*(-18) = 252

Now let's add up each pair of factors to see if one pair adds to the middle coefficient :

First Number	Second Number	Sum
1	252	1+252=253
2	126	2+126=128
3	84	3+84=87
4	63	4+63=67
6	42	6+42=48
7	36	7+36=43
9	28	9+28=37
12	21	12+21=33
14	18	14+18=32
-1	-252	-1+(-252)=-253
-2	-126	-2+(-126)=-128
-3	-84	-3+(-84)=-87
-4	-63	-4+(-63)=-67
-6	-42	-6+(-42)=-48
-7	-36	-7+(-36)=-43
-9	-28	-9+(-28)=-37
-12	-21	-12+(-21)=-33
-14	-18	-14+(-18)=-32

From the table, we can see that the two numbers and add to (the middle coefficient).

So the two numbers and both multiply to and add to

Now replace the middle term with . Remember, and add to . So this shows us that .

Replace the second term with .

Group the terms into two pairs.

Factor out the GCF from the first group.

Factor out from the second group.

Factor out

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

So factors to

this means factors to

So the final answer is
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