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### Inverse Function

```
Date: 8/2/96 at 1:58:23
From: Alfred T Chu
Subject: Inverse Function

Dear Dr. Math,

I have a questions:

z(x) = 4x + 15. How do I find the inverse function of   z(x)?

Sincerely,

Alfred
```

```
Date: 8/6/96 at 10:56:53
From: Doctor Jerry
Subject: Re: Inverse Function

Dear Alfred,

You want the inverse function of z(x) = 4x+15.

Usually, in inverse function questions, it is important to specify the
domain of the function.  For the function z, I assume the domain is R,
the set of all real numbers.  The function z gives y = z(x) values
when x values are given. The function zinv gives x values when y
values are given. So, suppose y = z(x) is given.  What value of x is
required for this?

To determine x, we solve the equation y = 4x+5 for x.  I feel certain
you can do this.  I find x = (y-5)/4.  So z inv(y) = (y-5)/4.

Some persons prefer the variable of a function to be x, so they prefer
to write zinv(x) = (x-5)/4 when describing the function zinv to
another person.

-Doctor Jerry,  The Math Forum
Check out our web site!  http://mathforum.org/dr.math/
```
Associated Topics:
High School Basic Algebra

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