Question

how can i factor out this completely: 28b^2-80b-128?

Answer 1

What is the GCF of 28, 80 and 128?

Answer 2

4

Answer 3

Factor out 4

4(7b^2 - 20b -32)

What multiplies to make 7?
What multiples to make 32? <------ be careful

Answer 4

1*7 1*32,2*16,4*8

Answer 5

but that's where i'm stuck!!!

Answer 6

look back at the last question. I am not sure you know why they added to -38. I think you might have hurried over that part. Maybe I am wrong?

For 4(7b^2 - 20b -32)

we have

4(7b ?)(b ?)

which ones should we choose for 32?

Answer 7

i don't know....

Answer 8

We need to get -20

If we take 4 and 8 notice

7 * 4 = 28
1 * 8 = 8 Notice 28 - 8 = 20
^ ^
| |
| |
| |
| multiplies to make 32
|
multiples to make 7

Answer 9

So we chose 4 and 8

4(7b +8)(b -4)

Answer 10

i ssee now