Question

Help!
f(x)=x^2-5 and g(x)=6x+2
(g x f)(x)

The answer that I get is 6x^3+2x^2-5x+10 and I know it's wrong. What did I do wrong?

Answer 1

(g x f)(x)
gf(x)
substitute f(x)=x^2-5
g(x^2-5)
substitute g(x)=6x+2
6(x^2-5)+2

Answer 2

ok where do i go from there?

Answer 3

is it\[(g\circ f)(x)\]or\[(g\times f)(x)\]?

Answer 4

the first one

Answer 5

then .Sam. Has show you the right path; just simplify.

Answer 6

right so 6x^3+2x^2-5x+10

Answer 7

\[(g\circ f)(x)=g[f(x)]\]so what is g(x) ?
write that out first

Answer 8

(6x+2)(x^2-5)

Answer 9

it is given in the problem that
"f(x)=x^2-5 and g(x)=6x+2 "
I just asked you what g(x) was...

Answer 10

oh 6x+2

Answer 11

cool, so now we want \(g[f(x)]\) which is just \(g(x)\) but replace all the x's that appear in g(x) with the expression for f(x)

Answer 12

6(x^2-5)+2

Answer 13

yes, now simplify :)

Answer 14

6x^2-30+12

Answer 15

where did you get 12 ?

Answer 16

i mean 8

Answer 17

...and where did you get the 8 from ?

Answer 18

6+2

Answer 19

where do you find 6+2 coming from
6(x^2-5)+2
?
watch your basic algebra, it'll bite you if you are not careful!

Answer 20

6x^2-30+2

Answer 21

i have no idea i hate math

Answer 22

that's correct above; you only distribute the 6 to what is in the parentheses.
of course we can still simplify this

Answer 23

6x^2+32

Answer 24

now you're just being lazy :P\[-30+2\neq32\]

Answer 25

6x^2-28

Answer 26

there we go :)
I can feel your satisfaction from here

Answer 27

bahaha yeah right. thank you!!

Answer 28

welcome!