Question

The domain for f(x) and g(x) is all real numbers. Let f(x) = 4x-1 and g(x) = x2-5x + 3
Find (fg)(x).

Answer 1

@Nnesha using FOIL, I got 4x^2+12x-x^2-3

Answer 2

4x^3+12x-x^2-3

Answer 3

but Mathway says the answer is 4x^3-21x^2+17x-3

Answer 4

could you tell me what I'm doing wrong?

Answer 5

I can't without any work shown.

Answer 6

what did you get after distribution(before simplifying )?

Answer 7

my guess is you forgot to multiply "all g(x) terms" with 4x

Answer 8

(4x)(x^2)=4x^3

(4x)(3)=12x

(-1)(x^2)=-x^2

(-1)(3)=-3

Put it all together, and the answer is:4x^3+12x-x^2-3

Answer 9

left `-5x` alone?

Answer 10

oh, sorry about that

so, 2. should've been (4x)(x^2-5x)?

Answer 11

or (4x)(5)=-20+x^2=21x^2

Answer 12

-21x^2

Answer 13

\[\color{blue}{4x-1}(x^2-5x+3)\]\[\color{blue}{4x}(x^2-5x+3)\color{blue}{-1}(x^2-5x+3)\]

Answer 14

how did you get -21?
what number did you add/subtract?

Answer 15

\(\color{#0cbb34}{\text{Originally Posted by}}\) @eviant
or (4x)(5)=-20+x^2=21x^2
\(\color{#0cbb34}{\text{End of Quote}}\)
something is missing ?
1st) you can't combine 20(constant) with x^2
2nd) -20+1 isn't -21

Answer 16

ugh, sorry, I suck at this stuff, what am I supposed to do instead?

Answer 17

I feel like you know how to do this stuff.
But you need to start writing it out to prevent mistakes

Answer 18

write like this
draw arrows
make sure to pay attention to the negative sign

Answer 19

once you done with the first term
distribute the 2nd term like that

Answer 20

1. 4x^3
2. -20x^2
3. 12x

Answer 21

that's correct!

Answer 22

try this one

Answer 23

1. -x^2
2. 5x
3. -3

Answer 24

awesome now we have to combine like terms
here is what we have
`4x^3-20x^2+12x-x^2+5x-3`

Answer 25

uh, so -20x^2-x^2=-21x^2?

Answer 26

and, 12x+5x=17x?

Answer 27

@Nnesha is this correct so far?

Answer 28

yes!

Answer 29

so, 4x^3-21x^2+17x-3?

Answer 30

yes. that's it!

Answer 31

good work1 o^_^o