I found an answer from www.quora.com

**Why is log not defined for negative values**? - Quora

In high school math, the natural **logarithm** \**log** x of a positive **number**
x>0 is **defined** to be the unique real **number** y such ...

For more information, see **Why is log not defined for negative values**? - Quora

I found an answer from www.khanacademy.com

Intro to **negative numbers** (video) | Khan Academy

Mysterious **negative numbers**! ... Your browser does **not** currently recognize any
of the video formats available. .... What does a **negative number** even **mean**?

For more information, see Intro to **negative numbers** (video) | Khan Academy

I found an answer from www.bbc.com

Positive and **negative numbers** - Revision 1 - KS3 Maths - BBC ...

Learn about and revise positive and **negative numbers** and how to add and
subtract or multiply and divide ... Positive numbers are written with **no** sign or a ' {
+} ...

For more information, see Positive and **negative numbers** - Revision 1 - KS3 Maths - BBC ...

I found an answer from www.britannica.com

**logarithm** | Rules, Examples, & Formulas | Britannica.com

**Logarithm**: **Logarithm**, the exponent or power to which a base must be raised to
yield a ... This is **not** all; the calculation of powers and roots can be simplified with
the use of logarithms. ... In the example of a **number** with a **negative** exponent,
such as 0.0046, one would look ... His **definition** was given in terms of relative
rates.

For more information, see **logarithm** | Rules, Examples, & Formulas | Britannica.com

I found an answer from math.stackexchange.com

Why are logarithms **not defined** for 0 and negatives? - Mathematics ...

Assume, we do have logarithms for **negative numbers** and zero and all ... No,
that's not right: no matter what the base b, **log**bx is **not defined** for ...

For more information, see Why are logarithms **not defined** for 0 and negatives? - Mathematics ...

I found an answer from en.wikipedia.org

Complex **logarithm** - Wikipedia

The principal **value** can be described also in a few other ways. ... Given z, the
polar form is **not** quite unique, because of the .... happens to Arg z as z
approaches a **negative** real **number** a.

For more information, see Complex **logarithm** - Wikipedia