- #1

applestrudle

- 63

- 0

## Homework Statement

f(x)= 2x + x^2

## Homework Equations

## The Attempt at a Solution

I don't know how to make x the subject

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- Thread starter applestrudle
- Start date

- #1

applestrudle

- 63

- 0

f(x)= 2x + x^2

I don't know how to make x the subject

- #2

Ray Vickson

Science Advisor

Homework Helper

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## Homework Statement

f(x)= 2x + x^2

## Homework Equations

## The Attempt at a Solution

I don't know how to make x the subject

You need to solve for x in the equation x^2 + 2x = y. This is a simple quadratic equation.

- #3

applestrudle

- 63

- 0

You need to solve for x in the equation x^2 + 2x = y. This is a simple quadratic equation.

Okay thank you!

I've got it:

X^2 +2x = y

add one so you get a quadratic that has a "squared"

x^2 +2x +1 = y + 1

solve quadratic:

(x+1)^2 = y + 1

x = (y+1)^-1/2 -1

f-1(x) = (x+1)^-1/2 -1

:)

Last edited:

- #4

Mark44

Mentor

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No.Okay thank you!

I've got it:

X^2 +2x = y

add one so you get a quadratic that has a "squared"

x^2 +2x +1 = y + 1

solve quadratic:

(x+1)^2 = y + 1

x = (y+1)^-1/2 -1

Starting from two lines above, you want to solve for x.

When you do this, don't forget that you need ± in there somewhere.

Note that the equation y = xf-1(x) = (x+1)^-1/2 -1

:)

- #5

skiller

- 237

- 5

You have raised to the power -1/2. Where did the negative sign come from?f-1(x) = (x+1)^-1/2 -1

:)

- #6

applestrudle

- 63

- 0

You have raised to the power -1/2. Where did the negative sign come from?

Sorry, mistake when I was typing! Thank you for pointing it out

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