Question

HELP Find the inverse of f(x) = 4x + 12

Answer 1

let y= 4x+12
can you isolate 'x' from this equation ?

Answer 2

start by subtracting 12 from both sides

Answer 3

-8x ?

Answer 4

nopes.
4x and 12 are not like terms, you cannot combine them

subtracting 12 from both sides of y=4x+12 will just give you
y-12 =4x
got this ?

Answer 5

ohh okay I understand that.

Answer 6

now divide both sides by 4
what u get ?

Answer 7

you get 1 and 3

Answer 8

12/4 = 3 is correct, but when you divide y-12 by 4, you get
\(\dfrac{y-12}{4}= \dfrac{y}{4}-\dfrac{12}{4}=\dfrac{y}{4}-3=\dfrac{4x}{4}=x\)
got this ?

Answer 9

yeahh I got it.

Answer 10

last step is to just exchange x and y, and you get your inverse!
\(f^{-1}(x)=\dfrac{x}{4}-3\)
thats it ...ask if any doubt in any step.

Answer 11

wait so whats x ?

Answer 12

and f

Answer 13

you need inverse of x, which we got as x/4 -3

Answer 14

right, but how do you find the answer ? just change them ad solve

Answer 15

go through the post again, all the steps are there, to get the final answer as x/4-3

Answer 16

You said the last step is to exchange x and y so is it this ? x/-3-4

Answer 17

I don't get that

Answer 18

ok, we had x = y/4 - 3
exchanging x and y we get

y= x/4 -3 which is your inverse function! :)

Answer 19

ohh that's simple I was way thinking this

Answer 20

yes, it is simple :) especially afte 2 or 3 question, you'll be able to do it mentally ;)

Answer 21

haha I hope so

Answer 22

I just tried that answer and it was wrong . /:

Answer 23

x/4 -3 is not taken ?
then lets not simplify it and keep it as
(x-12) /4
put this.

Answer 24

but in usual case, we need to simplify and so, x/4-3 should have been taken as correct :\

Answer 25

y = x / 4 - 3 I put this and I only have one more attempt to get it right . so should I type it in google ?

Answer 26

u sure the question is f(x) = 4x + 12 ?
then i would say, try
(x-12) /4

Answer 27

confirmed by wolfram
http://www.wolframalpha.com/input/?i=inverse+function+of+f%28x%29+%3D+4x%2B12

Answer 28

Yes I'm positive!!

Answer 29

then i am positive too, that the answer is (x-12)/4

Answer 30

Ok i'll try it I don't put x = ( x - 12 ) / 4 ? It says Please put a single space between terms to increase the chance of auto grade working. Such as y = x + 3 instead of y=x+3.

Answer 31

x = ( x - 12 ) / 4 ----- no
inverse of f(x) = ( x - 12 ) / 4

or \(f^{-1}(x)\) = ( x - 12 ) / 4

Answer 32

ok I will try it .

Answer 33

do u know how to do this ? The amount of money collected by a toll booth is represented by the function A(m) = $2.50m where m stands for the number of minutes after midnight.
What would be an appropriate domain for this function? Write your answer as an inequality and no spaces.

Answer 34

I got it wrong again !!