Log Base 2 of −1

Logarithm Calculator
Log base
x

What is log₂(−1)?

Answer

log2(−1)
does not exist

log2 is the log base 2.

2 raised to any power is a positive number, so the negative number −1 cannot be reached.

We look for y with 2y = −1.

Oxy1

The curve y = log2 x passes through (1, 0) and (2, 1) and rises: for x > 1 the log is positive, for 0 < x < 1 negative.

The graph exists only to the right of the y-axis: there is no point at x = −1.

Log of −1 in different bases
BaseNotationValue
eln(−1)does not exist
10log(−1)does not exist
2log₂(−1)does not exist

See Also

Log base 2 of nearby numbers

FAQ

What is log₂(−1)?

log₂(−1) does not exist

Does log₂(−1) exist in complex numbers?

Yes, in complex numbers: the principal value for x < 0 is log₂ x = (ln|x| + iπ) / ln 2, so log₂(−1) = iπ / ln 2 ≈ 4.5324i. Among real numbers it does not exist.

What does log without a base mean?

At school and on a calculator, log x without a base is the common log, base 10: log 100 = 2. In Python, math.log(x) is the natural log ln x; in Excel, LN is the natural log and LOG is base 10.