Need to be able to raise a negative number to a non-integer power

I can't answer your question definitively. But maybe I can add some rationale. First, VBA won't be able to do anything that the worksheet function and/or symbol can't do. That is, POWER and/or "^".

I would guess that Excel can cope with raising a negative number to an integer power because it can determine the sign. And it can raise a positive number to non-integer power because the result will always be positive.

Presumably, it can't calculate partial powers of negative numbers.

Can't even suggest a workaround. Even if you take out the -1, you can't raise that to the power of 2.2.

Part of the problem here is that exponentiation with a negative base and a rational exponent is somewhat challenging mathematically. Irrational exponents are even worse, if that is possible. When I approach these kinds of problems, I usually try to be clear exactly what mathematical situation I am working with and exactly what solution I expect from the problem. You might review the Wikipedia article for exponentiation for rational and real exponents: https://en.wikipedia.org/wiki/Expone...onal_exponents

You only give one example. How representative is this example? 2.2 (assuming this is 2.2000000000....) is a rational number (11/5), so can we assume that you will always be working with rational numbers for the exponent? Does your sheet include the numerator and denominator values somewhere, or will we need to come up with a formula to convert the decimal number into numerator and denominator? Or is the exponent potentially irrational, so that we cannot assume a rational exponent?

When I program this sort of thing in the spreadsheet, I end up choosing between different strategies:

1) The IMPOWER() function can usually calculate these without erroring. However, it also tends to return a complex number when the base is negative. Which is sometimes just fine when you only need an answer, but not very useful if you want the real solution and not a complex solution.

2) When I know there is a solution (because I know that the denominator of a rational exponent will always be odd), sometimes I will simplify the problem down to something like =SIGN(value)*POWER(ABS(value),exponent) or something similar. Obviously, this is not a generic solution, but it can work pretty well when I know the exponent will be rational and the denominator will be odd.

3) When I need more generic solutions, I often end up developing something based off of Euler's formula https://www.math.uvic.ca/~ibrahims/m...ex_numbers.pdf This often means acknowledging that there are multiple possible solutions and trying multiple solutions until I find the one I want.

I hesitate to provide a final solution, because I am not sure what kind of problem(s) you will need to solve based on only one example. Usually I end up working with one of those approaches, depending on what I know about the problems I expect to encounter.