Question

MEDAL AND FAN. Let f(x)=–5x + 3 and g(x) = 6x – 2. Find f *g and its domain.

I'm unsure of two things, do I FOIL? and how do I find the domain?

Answer 1

@ganeshie8 do you mind??

Answer 2

fxg =(-5x+3)(6x-2)=-30X^2+10X+18X-6= -30X^2+8X-6

DOMAIN=(-INFINITY , +INFINITY)

Answer 3

Okay, so what do you mean by infinity?

Answer 4

(-∞ , ∞ )

Answer 5

\[(-\infty, +\infty)\]

Answer 6

Okay.. but what do you mean by that?! I understand the multiplication but where does infinity come in?

Answer 7

The domain is.

Answer 8

@mikaylabean it means value of x can be from -infinty to + infinity. There is no specific domain

Answer 9

How do you determine that? Because I have a list of possible answers, and of course the right one is "all real numbers" but.. What about when theres an answer? How did he get that?

Answer 10

cuz that is a linear function and you know each linear function domain has a \[(-\infty, +)\]

Answer 11

Okay, so then how do you determine if it is linear? I haven't reviewed that in two years.

Answer 12

for instance, my next answer is "x-4" how would i determine that domain? Guys I'm really at a loss here.

Answer 13

@sangya21

Answer 14

http://coolmath.com/algebra/15-functions/06-finding-the-domain-01.htm

http://www.wikihow.com/Find-the-Domain-of-a-Function

Answer 15

Thank you.

Answer 16

Anytime :)

Answer 17

Would you mind helping me with a harder one? @sangya21

Answer 18

I can try.

Answer 19

Okay. Let f(x)=x^2+2 and g(x)=x+8/x Find (g*f)(-7)

Answer 20

Nothin?

Answer 21

(g*f)(-7) = g(f(-7)

\[g(f(x)) = \frac{ x^2 +16 +8 }{ x^2 +16 }\]
Put x = -7
\[g(f(-7)) = \frac{ (-7)^2 +24 }{ (-7)^2 +16 }\]

Answer 22

So the -7^2 would cancel right?

Answer 23

nopes. its not product but addition
\[g(f(-7) = \frac{ 49+24 }{ 49+16 }\]
\[g(f(-7) = \frac{ 73 }{ 65 }\]

Answer 24

Thats exactly what I got, but it's not one of the responses. The closest is 63/55

Answer 25

what are the other options?

Answer 26

\[-\frac{ 55 }{ 7 }, \frac{ 384 }{ 7 }, \frac{ 295}{ 49 }\]

Answer 27

I did wrong
\[g(f(x)) = \frac{ x^2 +2 + 8 }{ x^2 +2}\]
\[g(f(-7)) = \frac{ (-7)^2 +2 + 8 }{ (-7)^2 +2}\]
\[g(f(-7)) = \frac{ 59 }{ 51}\]

Answer 28

This is getting very frustrating v.v

Answer 29

It was 63/55

Answer 30

Okkk

Answer 31

sorry