# A to Z of Excel Functions: the IMSUB Function

18 January 2021

*Welcome back to our regular A to Z of Excel Functions blog. Today we look at the IMSUB function. *

**The IMSUB function**

An imaginary number is a complex number that can be written as a real number multiplied by the imaginary unit **i **(sometimes denoted **j**) which is defined by its property **i ^{2}** = −1. In general, the square of an imaginary number

**bi**is

**−b**. For example, 9

^{2}**i**is an imaginary number, and its square is −81. Zero is considered to be both real and imaginary.

An **imaginary** number **bi** can be added to a **rea**l number **a** to form a **complex number** of the form **a + bi**, where the real numbers **a** and **b** are called, respectively, the **real** part and the **imaginary** part of the **complex number**.

Sometimes you might wish to subtract one complex number from another. **IMSUB **returns the difference of two complex numbers in the **x + yi** or **x + yj** text format.

The **IMSUB **function employs the following syntax to operate:

**IMSUB(inumber1, inumber2)**

The **IMSUB** function has the following arguments:

**inumber1:**the first argument and represents the number from which to subtract**number2****inumber2:**this is also required. This is the complex number to subtract from**inumber1**.

It should be further noted that:

- you should use
**COMPLEX**to convert real and imaginary coefficients into a complex number **IMSUB**recognises either the**i**or**j**notation- if any of
**inumber1**or**inumber2**is a value that is not in the**x + yi**or**x + yj**text format,**IMSUB**returns the*#NUM!*error value - if any of
**inumber1**or**inumber2**is a logical value,**IMSUB**returns the*#VALUE!*error value - if any of
**inumber1**or**inumber2**is non-numeric,**IMSUB**returns the*#VALUE!*error value - if any complex number ends in +
**i**or -**i**(or**j**),*i.e.*there is no coefficient between the operator and the imaginary unit, there must be no space, otherwise**IMSUB**will return an*#NUM!*error - the difference of two complex numbers is given by:

Please see my example below:

*We’ll continue our A to Z of Excel Functions soon. Keep checking back – there’s a new blog post every business day.*

*A full page of the function articles can be found here. *