Question

Evaluate the composition
f(x)=2x-3 g(x)= x^2+2
solve (f*g)(3)
Can someone pls help? Not sure how the answer is 19 from this.

Answer 1

Im getting a quadratic equation when i solved this. I got 6x^3-9x^2+12x-18

Answer 2

well\[(f \times g)(x)=f(x) \times g(x)\] or formally\[[f(x)][g(x)]\]

Answer 3

and when i solved it i got something other than 19, so im not sure if you would want my help. lols

Answer 4

thats what i did and then i multiplied that by 3 but i don't see how they got 19 at all

Answer 5

(f*g) = (2x-3)(x^2+2)
=2x^3+4x-3x^2-6
(f*g)(3)=2(3^3)+4*(3)-3*(3^2)-6

Answer 6

you dont multiply it by 3, you plug in x=3

Answer 7

oh

Answer 8

hmm let me try it again real quick

Answer 9

hmm i got 33

Answer 10

yea, that should be it, but i guess if the book says 19, then we did something wrong.

Answer 11

:( dam. lol. ugh. i literally don't see anything that can be wrong.

Answer 12

sorry, couldn't be a help. i hope you can find your answer. lols

Answer 13

yea, no i mean you helped me in a way. Im gona try a few other problems and see if maybe they just put the wrong answer for that problem. Have a good one.

Answer 14

k, good luck

Answer 15

can i ask you another question though?

Answer 16

how would i do f(g(-3)) ?

Answer 17

oh ok, first you would plug -3 into the g(x) equation, and then you plug whatever you got for g(x), and plug it in in f(x).

Answer 18

oh

Answer 19

ok hold on 1 sec pls :) lol

Answer 20

sure

Answer 21

ok ok i got 19 and it says the answer for that is 19 as well so im thinking maybe they put the wrong answer for the first one, lol.

Answer 22

yay. whohoo!

Answer 23

will u stay for a few more i have?

Answer 24

sure, im stuck in my hw problem, just staring at it like a zombie, so why not

Answer 25

lol, thanks man. maybe i can help? what is it?

Answer 26

lol its calculus

Answer 27

oh dam man. lol. Im in pre cal in college. Slacked off a little in high school. lol. At 1 in the morning though, its a little hard to do this lol. I haven't done this since last year.

Answer 28

lol. ur est, so lets try to solve your other questions too. gotta brush my teeth and go to sleep soon. im pst

Answer 29

oh ok. Yea. lol. ok hopefully im doing the other ones right but for (fxf)(-2) i got 49 and it says the answer is -17

Answer 30

is it still the same function for f(x) which is 2x-3?

Answer 31

yea

Answer 32

so its very similar to f(g(x)), except you just plug in -2 in 2x-3, which u will get -7, and plug in -7 in 2x-3, wchi is -17.

Answer 33

ur just using f(x) twice. no biggie

Answer 34

oh my god, lol. I just thought you took the -7 and multiplied it by -7 because thats what i thought fxf was. ugh man. Need to refresh on my math skills.

Answer 35

its ok. we always get stuck. thats what learning is all about. getting stuck. hehe

Answer 36

yea, lol. and thanks for the medal. umm for g(g(1/2)) am i just solving for g of 1/2 and then plugging that into g?

Answer 37

yup

Answer 38

ok i got whatever 2.25 squared plus 2 equals to.

Answer 39

i suggest you put it in fractions, becuase precalc + is all about real numbers, no decimals.

Answer 40

i mean 4.25 omg. srry. im sick and tiered and.. literally doing math at 2 am.

Answer 41

i don't have a calc on me though. except my phone and comp. But they don't have the advanced functions.

Answer 42

would that be right though?

Answer 43

lemme do it on the drawing pad