Question

HELP PLSS Let F(x)=5 over X and g(x)=2x^2+5x What two numbers are not in the domain of f o g?

Answer 1

what do you think f o g means?

Answer 2

like the x of both equations?

Answer 3

no. f o g means f[ g(x) ] <-- so what does this also mean?

Answer 4

f=g(x)?

Answer 5

no. If you have f(x), what would, say, f(3) means?

Answer 6

x=3

Answer 7

exactly. So for every x you see, you replace x for 3, correct?

Answer 8

yes

Answer 9

using the analogy, what do you now think f[ g(x) ] means?

Answer 10

like x is the number that u will plug in for g and f

Answer 11

so in this case, f(x) = 5/x.
What would you do to f[ g(x) ] ?

Answer 12

like my answer choices are all 0, and then Ais -5 over 2 B is -2 over 5 C is 2 over 5 and D is 5 over 2 so I'm confused

Answer 13

???

Answer 14

i'm trying to help you get the answer.

so f(x) = 5/x, f[ g(x) ] would means 5/g(x) right? for every x in f, you replace x with g(x). yes?

Answer 15

yes

Answer 16

ok, if you do so, what is the equation would you have?

Answer 17

umm idk??

Answer 18

im so confused???

Answer 19

well you have f(g(x)) = 5/g(x) correct?

what is the equation of g(x)?

Answer 20

its 2x^2+5x

Answer 21

good. Then what is 5/g(x) look like?

Answer 22

5 over 2x^2+5x ???

Answer 23

excellent.
f(g(x)) = 5/(2x^2 + 5x)

what would you do next?

Answer 24

would u cross out the 5??

Answer 25

no you can not.
what do you notice you can do with the denominator?

Answer 26

simplify

Answer 27

can you?

Answer 28

how would u do that

Answer 29

you can't. That's nothing can simplify. What kind of function is the denominator? also known as g(x)

Answer 30

idk what function it is ?

Answer 31

it's quadratic function yes?

Answer 32

yes cuz u put a 0 at the end right?

Answer 33

what 0?

Answer 34

like equal to zero

Answer 35

so you're trying to solve x^2 + 5x = 0 ?

Answer 36

isn't 2x^2+5x=0

Answer 37

????

Answer 38

oh you're right. 2x^2 + 5x = 0

Answer 39

so what would that be ????

Answer 40

can it be factor?

Answer 41

yea x(2x+5)

Answer 42

very good. x (2x + 5) = 0

what would you do next?

Answer 43

ohhh its 0, -5 over 2

Answer 44

very good. 0 and -5/2, but why are they not in the domain though?

Answer 45

because its negative ??

Answer 46

???

Answer 47

no what is g(0) and g(-5/2) ?

Answer 48

idk

Answer 49

well, we got x = 2 and x = -5/2 by setting 2x^2 + 5x = 0.
so when you plug 2 or -5/2 back in for x, what should you get?

Answer 50

wait so the answer is 0,-5 over 2 that is not the domain??

Answer 51

Correct. 0 and -5/2 are the answers. But I want to know why they're not part of the domain

Answer 52

because if u plug them in it won't give u x?

Answer 53

plug 0 or -5/2 in what?

Answer 54

in g of x

Answer 55

?????

Answer 56

correct, so what would g(0) and g(-5/2) equal?

Answer 57

0

Answer 58

very good. then what is 5/g(0) of 5/g(-5/2) ?

Answer 59

0, -5 over 2

Answer 60

???

Answer 61

????

Answer 62

g(0) = 0, g(-5/2) = 0 yes?

Answer 63

yes

Answer 64

0

Answer 65

5/0 is 0?

Answer 66

yea undefiend

Answer 67

that's right. When x = 0 or -5/2, g(x) would be 0, but you can *not* divide by 0. Therefor, 0 and -5/2 are not part of the domain.

Answer 68

ohhhh thank u man how can i give u a medal u helped me a lot!!

Answer 69

just click "Best Response"