Question

how can this be factored? : 7x^2+16x-15

Answer 1

break down the middle term

\[7x^2 + 21x - 5x - 15\]
group
\[(7x^2 + 21x) - (5x + 15)\]
factor out
\[(7x(x+3) - 5(x+3)\]
do you see it now?

Answer 2

why did you pick 21 and -5? because they add to 16?

Answer 3

yup

Answer 4

and because 21 is a factor of 7...and 5 is a factor of 15

Answer 5

is that last term supposed to be x+3 or x-3?

Answer 6

x+3

Answer 7

i factored out -5

Answer 8

right so -5 * 3 would be -15 dont we want +15?

Answer 9

but the question says -15

Answer 10

ok so you revert back to the question on the final factoring

Answer 11

revert back? no

Answer 12

i kept on factoring

Answer 13

oh sorry i see it now

Answer 14

it was -15 all along

Answer 15

yes

Answer 16

this question is to find the zeros of a polynomial and the books answer s are 5/7,3,-3

Answer 17

3 answers?

Answer 18

that cant be

Answer 19

3 is not a zero

Answer 20

it's just -3

Answer 21

would you like me to show you?

Answer 22

maybe im confused, it says find the solution set of 7x^3-5x^2-63x+45 is 5/7,3,-3

Answer 23

youre right the zero is three

Answer 24

that's a different thing lol

Answer 25

ya sorry im so burnt out on this stuff

Answer 26

zero was the step before

Answer 27

step before what?

Answer 28

before what we just did

Answer 29

we didnt do any zeroes o.O

Answer 30

you were just asking for factoring..

Answer 31

i know i already did that on my own, that doesnt matter now

Answer 32

so what's the question now?

Answer 33

my question now is how did 7x(x+3)-5(x-2) become 5/7,3,-3

Answer 34

it's not

Answer 35

5/7, 3, -3 are zeroes to a different problem

Answer 36

thats the answer for "find the solution set"

Answer 37

find the solution set of 7x^3-5x^2-63x+45 is 5/7,3,-3

Answer 38

see? different problem

Answer 39

we were doing 7x^2+16x-15

Answer 40

sorry i should have set this up better. its all the same problem. the factoring trouble was after i had broken the big polynomial down through division

Answer 41

ahh

Answer 42

do you know the zeroes of 7x^2+16x-15 though?

Answer 43

no

Answer 44

if you do the factoring a while ago

7x(x+3) - 5(x+3)

you get

(x+3)(7x-5)

Answer 45

to get the zero..you equate the factors to zero

Answer 46

ohhh got it

Answer 47

when x + 3 = 0

x = -3

Answer 48

when 7x - 5 = 0

7x = 5

x = 5/7

Answer 49

then the other zero which is x = 3

i assume it's the one you divided by

(x - 3)

Answer 50

yes sir

Answer 51

so if you equate x - 3 to zero

x = 3

those are your zeroes

-3. 5/7 and 3

Answer 52

ya perfect thank you

Answer 53

<tips hat>

Answer 54

hey while i have you, what incentive is there for teachers like you to help on this site?

Answer 55

is there pay involved? or an internship or something?

Answer 56

well i have to go but i will tell you that im no teacher...there's no pay..no internship...no something...this is purely voluntary

Answer 57

i for one do it for the love of teaching lol. i like teaching people how to do stuffs

Answer 58

haha well i really appreciate it.

Answer 59

i believe a lot others do it for the love of teaching as well ^_^ some do it as give and take. ithis site has helped me in my academics as well so i teach too

Answer 60

well im going now. bye

Answer 61

thanks again bye!

Answer 62

@lgbasallote , you made a parenthetical mistake :P