Scientific notation and negative numbers My daughter is learning scientific notation in school, and her textbook says something to the effect of this:

Scientific notation is a method of writing numbers as the product of
two factors where the first factor is a number greater than or equal
to 1 but less than $10$ and the second factor is a power of $10$.

The teacher is taking this to mean that you cannot express a negative number in scientific notation. So that e.g.
$$-4 \times 10^{50}$$
would not be valid scientific notation because $-4$ is less than $1$.
Is there such a view of scientific notation? It certainly doesn't jive with my memory (or wikipedia), or is that description just deficient, and should better read:

Scientific notation is a method of writing numbers as the product of
two factors where the first factor is a number whose absolute value is greater than or equal
to 1 but less than 10 and the second factor is a power of $10$.

And if it is a legitimate view, how do you express negative numbers in scientific notation?
You are right. The textbook and teacher are wrong.

Scientific notation is where numbers are written in the form $a × 10^b$ where $a ∈ ℝ$ and $b ∈ ℤ$.

Normalized scientific notation also stipulates that $1 ≤ |a| &lt; 10$.

$\therefore \;\; -4 × 10^{50}$ is correct normalized scientific notation, as common sense would dictate.
You would write the problem as: $|-4| \times 10^{50}$, or $4\times 10^{50}$. Your teacher is right, you cannot express a scientific notation as a negative number. It has to be a number greater than or equal to one, but less than 10. The absolute value would be taken, therefore, giving you $4 \times 10^{50}$. I just did one like this in college Chemistry. Thanks! MB