SOLUTION: Finding an inverse formula of f(x) = 9-4x First I replaced f(x) with y: y=9-4x then i switched y with x: x=9-4y then i solved for y x-9 = -4y (x-9)/-4 = y This is a final r

Algebra ->  Average -> SOLUTION: Finding an inverse formula of f(x) = 9-4x First I replaced f(x) with y: y=9-4x then i switched y with x: x=9-4y then i solved for y x-9 = -4y (x-9)/-4 = y This is a final r      Log On


   

Question 193144: Finding an inverse formula of f(x) = 9-4x
First I replaced f(x) with y: y=9-4x
then i switched y with x: x=9-4y then i solved for y
x-9 = -4y
(x-9)/-4 = y
This is a final review exercise and the possible solutions are as follows, but none are like mine:
f-1(x) = 9+4x
= 1/(9-4x)
= (x-4)/1
= (9-x)/4
the fourth one would be the closest, but is not the same as I got...
What did I do wrong?
Found 3 solutions by nerdybill, Earlsdon, stanbon:
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
Your answer:
(x-9)/-4 = y
.
Is just fine.
.
Notice the -4 on the denominator. What if we wanted to make it positive? To do this, we would multiply by -1/-1:
[-1/-1][(x-9)/-4] = y
-(x-9)/4 = y
(-x+9)/4 = y
(9-x)/4 = y
.
Which is the last choice.

Answer by Earlsdon(6294) About Me  (Show Source):
You can put this solution on YOUR website!
Your answer is absolutely correct but in a slightly different form from the fourth entry on your list of possible answers!
Your answer:
%28x-9%29%2F-4 this can be arranged as follows:
%28%28x-9%29%29%2F-4+=+-%28%28x-9%29%29%2F4=%28-x-%28-9%29%29%2F4+=+%28%28-x%2B9%29%29%2F4=highlight%28%28%289-x%29%29%2F4%29

Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
You did nothing wrong.
---
You applied the negative to the denominator; they applied it to the
numerator.
"d" is the correct answer.
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Keep in mind the following -(a-b) = b-a
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Cheers,
Stan H.