# Cube rooting a negative number does not work?

I tried using this formula for cube rooting but it doesn't seem to work.

``````=ROUND(C38^(1/3))
``````

The value of `C38` is `-2`.

I'm getting the following error:

Imaginary numbers are not supported in real sheets.

Shouldn't cube roots logically work without being imaginary, whether it's negative or positive?

• Could you share the spreadsheet with us? Or another spreadsheet demonstrating the problem? – Vidar S. Ramdal Jan 21 '14 at 8:48

I am not sure why it's not supported but you can bypass it this way:

`=ROUND(IF(C38 < 0,-1*ABS(C38)^(1/3),C38^(1/3)))`

That would be your formula for rounding a cube root.

• Wow it actually works thanks :) – puretppc Jan 21 '14 at 22:46

Use the following notation to perform these types of calculations.

## Formula

``````=minus(a^(b/c))
``````

## Research

I thought it was a rather odd behavior of Google Spreadsheets and therefore I started to investigate the situation.

It started by performing the calculation in the Google Calculator: There, the notation

``````-2^(1/3)
``````

was re-written to

``````-(2^(1/3))
``````

This solves your problem immediately. Entering the last formula (with `ROUND()`) in Google Spreadsheets, will give you : -1. But why?

## Why

In the first reference, Dr. Math is explaining the matter in detail. Bottom line is that the calculation is returning an imaginary number, like the cube root of -1.

To avoid these calculations, the minus is simply extracted from the calculation and "added" afterwards.