# Homework Help: Solving for a variable inside the error function?

1. May 2, 2013

### channel1

i need to solve for a variable inside the error function on excel, is there an opposite function i can use to accomplish this?
example: y = sqrt(x-t) -> x = t+y^2
except instead of a sqrt( ) I have erf( )

**this is not a math class so I don't have to get into breaking it down into the integration, I'm just looking for a way to quickly rearrange the equation in excel (I'm posting this here because I've only come into contact with the error function in physics classes where we DID use the integration/taylor series)

2. May 2, 2013

### Staff: Mentor

There is an inverse, denoted erf-1, but it won't be that simple to use, as it's typically given as a Maclaurin series. See this wiki article.

3. May 2, 2013

### Office_Shredder

Staff Emeritus
Depending on the context you could use excel solver to do this

4. May 2, 2013

### channel1

does erf^-1(erf(function)) = function?

5. May 2, 2013

### channel1

^ wolframalpha says yes, I think this may solve everything, thanks!

6. May 2, 2013

### channel1

damn, excel doesn't recognize the inverse error function, is there a way around that?

7. May 2, 2013

### Ray Vickson

As others have indicated, you can use the EXCEL Solver tool. Alternatively, you can consult handbooks of mathematical functions and find approximate formulas for erf^(-1) of various degrees of accuracy, then program these into your calculator/computer.

Last edited: May 2, 2013