Find inverse for f(x)= x/(1+x)

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In summary, the conversation is about finding the inverse function of a given function, f(x)= x/(1+x), and solving the equation for the inverse function. The conversation includes various attempts and steps in solving the problem.
  • #1
jimjames
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Homework Statement


Show that the functions f are one-to-one and calculate the inverse function.

Homework Equations


f(x)= x/(1+x) (It is the equation I am having trouble with)

The Attempt at a Solution


I know the solution is y= x/(1-x) But no idea how to solve it.

My attempt:
x(1+y)=y or x+xy=y

y+y=x/x
 
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  • #2
jimjames said:

Homework Statement


Show that the functions f are one-to-one and calculate the inverse function.

Homework Equations


f(x)= x/(1+x) (It is the equation I am having trouble with)

The Attempt at a Solution


I know the solution is y= x/(1-x) But no idea how to solve it.

My attempt:
x(1+y)=y or x+xy=y
Start with ##y = \frac x {1 + x}##
What's the first thing you need to do?
jimjames said:
y+y=x/x
I'm not sure what you did here.
 
  • #3
Where did you get y = x/(1+x) ?

What i normally do is
f(x) = x/(1+x) <=> x=f^-1(y)
f(y) = y/(1+y) <=> y=f^-1(x)

x=y/(1+y)
y=x+xy

And now I'm stuck
 
  • #4
jimjames said:
Where did you get y = x/(1+x) ?

What i normally do is
f(x) = x/(1+x) <=> x=f^-1(y)
f(y) = y/(1+y) <=> y=f^-1(x)
The above doesn't help you with this problem. All you're doing is manipulating symbols.
jimjames said:
x=y/(1+y)
In the line above, all you did was switch x and y.
jimjames said:
y=x+xy
How did you get the equation above?
jimjames said:
And now I'm stuck
Start with y = ##\frac x {1 + x}##

For this problem DO NOT switch the variables x and y.
DO solve for x in the equation just above. In other words, x should appear only on one side of the equation.
 
  • #5
y(1+x)=x
1+x=x/y
 
Last edited:
  • #6
jimjames said:
y(1+x)=x
1+x=x/y
OK.

Now divide both sides by x.
 
  • #7
jimjames said:
Where did you get y = x/(1+x) ?
That's the function you're trying to find the inverse of.
Multiplying both sides of this equation by 1 + x gives you the equation just below.
jimjames said:
y(1+x)=x
1+x=x/y
SammyS said:
OK.

Now divide both sides by x.
It's probably simpler to expand y(1 + x), get all terms that involve x on one side, and then isolate x.
 
  • #8
jimjames said:

Homework Statement


Show that the functions f are one-to-one and calculate the inverse function.

Homework Equations


f(x)= x/(1+x) (It is the equation I am having trouble with)

The Attempt at a Solution


I know the solution is y= x/(1-x) But no idea how to solve it.

My attempt:
x(1+y)=y or x+xy=y

y+y=x/x

Why do you call this a "transcendental function"? It is just about as far from transcendental as you can get.
 
  • #9
Ray Vickson said:
Why do you call this a "transcendental function"? It is just about as far from transcendental as you can get.
I changed the title a while ago for that very reason.
 
  • #10
jimjames said:
Where did you get y = x/(1+x) ?

What i normally do is
f(x) = x/(1+x) <=> x=f^-1(y)
f(y) = y/(1+y) <=> y=f^-1(x)

x=y/(1+y)
y=x+xy

And now I'm stuck
Subtract xy from both sides: y- xy= y(1-x)= x
 
  • #11
Managed to solve this late yesterday.
Thanks for trying to help.:smile:
 

Related to Find inverse for f(x)= x/(1+x)

1. How do I find the inverse for f(x)= x/(1+x)?

To find the inverse for f(x), you need to follow a few steps. First, replace f(x) with y. Then, switch the x and y variables. Next, solve for y. Finally, replace y with f^-1(x) to get the inverse function.

2. Can the inverse of f(x)= x/(1+x) be simplified?

Yes, the inverse of f(x) can be simplified. After switching the x and y variables and solving for y, you may need to use algebraic manipulation to simplify the expression. However, the resulting function will still be the inverse of f(x).

3. How do I graph the inverse of f(x)= x/(1+x)?

To graph the inverse of f(x), you can use the original function's graph and reflect it over the line y=x. This means that the x and y coordinates will switch places. Additionally, the inverse function will have the same shape as the original function, but it will be a mirror image.

4. Is the inverse of f(x)= x/(1+x) a one-to-one function?

Yes, the inverse of f(x) is a one-to-one function. This means that each input has only one output and each output has only one input. This property is necessary for a function to have an inverse.

5. How can I use the inverse of f(x)= x/(1+x) to solve equations?

You can use the inverse of f(x) to solve equations by plugging in the value of x into the inverse function and solving for y. This will give you the solution to the equation. Additionally, you can use the inverse function to check if a given solution is correct by plugging it into the original function and seeing if it equals the given value of x.

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