Why am I getting
#NUM error in Excel when trying to input:
It works fine on Wolfram Alpha..
You need to use imaginary number functions for your equation. Excel expects real numbers for its operations; so it returns
#NUM when an imaginary number is created and you didn't specify an imaginary number function.
The fourth root of a negative number will be a complex (real + imaginary) number in the form:
a+bi that your Excel formula is unable to manage.
You have to rewrite your formula to:
That will give you the result:
The same as Wolphram Alpha