# Algebra II Honors Homework Help

1. Dec 9, 2011

### darshanpatel

The inverse of f(x)= k(-x^3 -4x -9) is a function and f^-1(7)=1. What is the value of k?

Work is a picture: http://tinypic.com/view.php?pic=29xj4i8&s=5

Mod note: Too large picture deleted

Last edited by a moderator: Dec 9, 2011
2. Dec 9, 2011

### SammyS

Staff Emeritus
Hello darshanpatel. Welcome to PF.

Here's a hint: If $\displaystyle f^{-1}(7)=1\,,$ then what is $\displaystyle f(1)\,?$

Note: When a moderator of these forums sees the size of that image, he/she will likely delete it.

3. Dec 9, 2011

### darshanpatel

The y is from exchanging the x and y's to get the inverse, also can you please help me and not hint lol.

4. Dec 9, 2011

### SammyS

Staff Emeritus
LOL indeed!

Read the rules of these Forums.

By the way: The hint I gave should lead you directly to the solution.

5. Dec 9, 2011

### Staff: Mentor

Picture copied.

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6. Dec 9, 2011

### SammyS

Staff Emeritus
Thanks Evo !!!

7. Dec 9, 2011

### darshanpatel

I dont understand the hint... Do I plug it directly in or something?

Also Another PF mod or something said it was ok...

8. Dec 9, 2011

### SammyS

Staff Emeritus

9. Dec 9, 2011

### darshanpatel

So I plug 1 into x variables and make whole equation = to 7?

10. Dec 9, 2011

### SammyS

Staff Emeritus
Yes. Then solve for k.

11. Dec 9, 2011

### darshanpatel

Thank you, you are really smart. :)

12. Dec 9, 2011

### Staff: Mentor

If it is much larger than 800 x 600 pixels, the moderators will likely delete it.

13. Dec 10, 2011

### darshanpatel

ok, thanks...