Question

Factor -3x^2 - 4x + 15
Please explain!

Answer 1

you can break down the middle term into \[-(3x^2 + 4x - 15) \implies -(3x^2 - 5x + 9x - 15)\]
does that help?

Answer 2

Not at all, I'm sorry! This is the one thing I can never figure out

Answer 3

but...you get how -3x^2 - 4x + 15 became -(3x^2 + 4x - 15)?

Answer 4

Hmm, I think so yeah

Answer 5

what about when i turned it into -(3x^2 - 5x + 9x - 15)...did you get that?

Answer 6

Nope

Answer 7

well...do you agree that 9x - 5x = 4x?

Answer 8

Mhm!

Answer 9

so do you get how -(3x^2 + 4x - 15) became -(3x^2 - 5x + 9x - 15)?

Answer 10

Why would you use those two numbers instead of anything else?

Answer 11

good question

Answer 12

because of this next step im about to do

Answer 13

Oh okay! Continue c:

Answer 14

\[-(3x^2 - 5x + 9x - 15) \implies -(x(3x - 5) + 3(3x - 5))\]

do you get what happened there?

Answer 15

Yup!

Answer 16

wonderful. now do you see that 3x - 5 is common above? that means i can factor it out \[\implies -(3x - 5)(x+3)\]

Answer 17

do you get what happened there?

Answer 18

Oh, yes! Thank you (:

Answer 19

welcome