Question

factor 9a^3+15a^2-36a

Answer 1

Start with greatest common factor GCF

Answer 2

i did that 3a

Answer 3

3a(3a^2+5a-12a)

Answer 4

nice... now I would use ac method

Answer 5

ac would be (3)(-12) to get the number that you must find factors for that might add up to the middle term.

Answer 6

yea i did -9 and 4

Answer 7

-36
ignoring signs for a moment....
1 and 36... the sum or difference doesn't get 5
2 and 18... the sum or difference doesn't get 5
3 and 12... the sum or difference doesn't get 5

Answer 8

yeah

Answer 9

now split the middle term into -4a + 9a to make the 5a

Answer 10

thats what i did. i got stuck at the last part.

Answer 11

then it is a grouping problem

Answer 12

\[3a(3a ^{2}-4a+9a-12)\]

Answer 13

\[3a(a(3a-4)+3(3a-4))\]

Answer 14

3a-4 is common to both of the inside terms, pull it out in front of the others

Answer 15

which leaves behind a+3

Answer 16

i got that but i dnt understand how to put it as the answer

Answer 17

3a(3a-4)(a+3) should be the fully factored form

Answer 18

If it is set equal to zero... you can solve

Answer 19

ok yes that looks more like it. I was having a hard time grouping.

Answer 20

thank you

Answer 21

you're welcome :)