Scientific notation and negative numbers

Question

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?

Your reformulation is still inadequate, as it can't express $0$. — Chris Eagle, Dec 07 '12 at 08:14
Maybe the teacher can watch this: http://www.youtube.com/watch?v=0Elky_dDak0 — Amzoti, Dec 07 '12 at 09:34
@ChrisEagle, does Zero exist in science? has it been measured to perfect(mathematical) precision? Don't Probabilities get just incredibly small, never 'reaching' Zero. — Elements In Space, Jan 20 '13 at 17:23
@ChrisEagle: when do you need to write $0$ in the scientific notation ? And with what exponent ? — , Sep 25 '15 at 13:51
@YvesDaoust you can express zero in scientific notation as $ 0 \times 10^0 $ if you really want to use scientific notation. — Warren Hill, May 22 '16 at 18:29
@YvesDaoust one situation where I have wanted zero in scientific notation was as part of an engineering test setup where results were logged to a PC. Having all results in scscientific notation made getting results easier to parse. Zero was +0.0000E+00 — Warren Hill, May 24 '16 at 11:49

score 7 · Accepted Answer · answered Feb 27 '15 at 12:01

7

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 $1 ≤ |a| < 10$.

$\therefore \;\; -4 × 10^{50}$ is correct normalized scientific notation, as common sense would dictate.

answered Feb 27 '15 at 12:01

Zaz

1,544

Everyone is right, there is no incompatibility ! – Sep 25 '15 at 16:08
@YvesDaoust: According to the textbook definition “and the second factor is a power of 10”, $7×1000000$ is scientific notation. This is incorrect. “The teacher [says] you cannot express a negative number in scientific notation.” This is also wrong: $−1×10^0$ expresses $-1$ in scientific notation. – Zaz Sep 25 '15 at 17:50
1

I wasn't clear. $1\times 10^0$ is scientific notation; according to the teacher's definition, $-1\times 10^0$ is not scientific notation. But it is a valid number anyway: the negative of $1\times 10^0$. These two points of view are quite reconciliable. – Sep 25 '15 at 19:07
@YvesDaoust: Sorry if I seemed short. Your point that $(-a)b = -(ab)$ is a good one, but from my point of view it only makes the statement “you cannot express a negative number in scientific notation” even more meaningless. Ahhh... after considering the question “Can you express a negative number in decimal?” I think I see your point perfectly. Technically the answer is no, for that you'd need a negative base or $-$. In any case, I think what the teacher said is unhelpful, certainly if she didn't also explain that you could stick a minus sign in front of it to make it negative. – Zaz Sep 26 '15 at 00:30
My point is that what the teacher said is harmless. – Sep 26 '15 at 08:12
@YvesDaoust: To an experienced mathematician perhaps, but not to the average high-schooler who is asked on the test to “Express the charge of an electron in scientific notation.” There are 2 possibilities here: The teacher is wrong and the answer is $-1.602×10^{-19}$, or the teacher is correct, and there is no right answer. The fact that $-1.602×10^{-19}$ is a number regardless of how you define standard notation is moot. – Zaz Sep 26 '15 at 13:14
2.292406495696726e-05 is the same as 0.00002292406, so is -2.7180886552000747e-15 the same as -0.000000000000002718088? – Edison Jul 03 '22 at 12:49
@Edison: Other than the rounding error, yes. – Zaz Jul 03 '22 at 23:55

score 3 · Answer 2 · 2015-09-25T16:07:42.297

There is no problem having a negative number shown in scientific notation, computers and calculators have been doing this for ages. The quote from the textbook shouldn't be taken too literally as they were probably thinking of the magnitude of the number and forgot about this trivia.

In any case, the problem collapses if you read $-4\cdot10^{50}$ as $-(4\cdot10^{50})$. The expression inside the parentheses is a valid number written in the scientific notation, and there is no reason to forbid taking the opposite. (Though the whole expression itself cannot be called a "number written in the scientific notation" if you apply the definition as it stands.) Remember that by usual rules of precedence, $-a\cdot b$ is understood as $-(a\cdot b)$.

As regards myself, I would not even object against notations like $4000\cdot10^{47}$ or $0.004\cdot10^{53}$ which still make sense (denormalized scientific notation). — , Sep 25 '15 at 12:58

score 1 · Answer 3 · answered Sep 26 '15 at 01:14

1

By now you may have noticed that, if put to a vote, "Yes, you can use negative numbers too." would win but not by a unanimous vote. There was a time, when people used slide rulers, that scientific notation was needed to perform calculations. It still is now, but not nearly as much. Now it's just a simple way to represent really large and really small numbers. Once your daughter gets out of that class, I don't think anyone will complain if she expresses negative numbers using scientific notation.

answered Sep 26 '15 at 01:14

Steven Alexis Gregory

27,619

So you are saying that for slide rulers there were no negative numbers? – Yishai Sep 27 '15 at 01:16
@Yishai. My God. Am I really that old? No, they were not necessary. Slide rules were made, mostly, to multiply numbers. You had to work out the powers of 10 and the sign of the product. – Steven Alexis Gregory Sep 27 '15 at 02:41

score 0 · Answer 4 · edited Aug 04 '20 at 09:33

Scientific notation is a way to shorten a value/measure of a thing in reality. For example: Mass of an atom of Oxygen is $0.0000000000000000000002677931574$ gram. It is a positive number, but extremely small. To be easier for writing this value, scientists created a kind of notation, called scientific notation by using exponent/power of $10$. Therefore, the above number can be written such as $2.677931514 x 10^{-22}$ ($10$ power to negative $22$) So, do not get confused with a negative number of it. Scientific notation is NEVER used for a negative number. An extremely small negative number can borrow the scientific notation to shorten its writing, but the concept of "scientific notation" is just for a positive number of the value of the real things in the REALITY!

Your answer is quite difficult to read, as it lacks niceties such as paragraph breaks and proper mathematical formatting. It would likely be better received after some minor editing. — Xander Henderson, Dec 03 '17 at 00:00

score -4 · Answer 5 · edited Sep 25 '15 at 12:19

-4

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

edited Sep 25 '15 at 12:19

BLAZE

1

answered Jan 29 '15 at 22:20

user211634

1

Sorry, I'm not following what you are trying to say. – Yishai Jan 29 '15 at 22:33
To be more specific, I'm not seeing how you are expressing (or distinguishing) a negative. – Yishai Jan 29 '15 at 22:40

Scientific notation and negative numbers

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