10.5 Integer exponents and scientific notation  (Page 3/7)

In the next two examples, we’ll use the Power Property and the Product to a Power Property .

To simplify a fraction, we use the Quotient Property .

Simplify: $\frac{r^5}{r^{\mathrm{-4}}}.$

Solution

Use the Quotient Property, $\frac{a^m}{a^n}=a^{m-n}$ .
Simplify.

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Convert from decimal notation to scientific notation

Remember working with place value for whole numbers and decimals? Our number system is based on powers of $10.$ We use tens, hundreds, thousands, and so on. Our decimal numbers are also based on powers of tens—tenths, hundredths, thousandths, and so on.

Consider the numbers $4000$ and $0.004.$ We know that $4000$ means $4\times 1000$ and $0.004$ means $4\times \frac{1}{1000}.$ If we write the $1000$ as a power of ten in exponential form, we can rewrite these numbers in this way:

When a number is written as a product of two numbers, where the first factor is a number greater than or equal to one but less than $10,$ and the second factor is a power of $10$ written in exponential form, it is said to be in scientific notation.

It is customary in scientific notation to use $\times$ as the multiplication sign, even though we avoid using this sign elsewhere in algebra.

Scientific notation is a useful way of writing very large or very small numbers. It is used often in the sciences to make calculations easier.

If we look at what happened to the decimal point, we can see a method to easily convert from decimal notation to scientific notation.

In both cases, the decimal was moved $3$ places to get the first factor, $4,$ by itself.

• The power of $10$ is positive when the number is larger than $1\text{:}4000=4\times {10}^3.$
• The power of $10$ is negative when the number is between $0$ and $1\text{:}0.004=4\times {10}^{-3}.$

Write $\mathrm{37,000}$ in scientific notation.

Solution

Step 1 : Move the decimal point so that the first factor is greater than or equal to 1 but less than 10.
Step 2 : Count the number of decimal places, $n$ , that the decimal point was moved.	3.70000 4 places
Step 3 : Write the number as a product with a power of 10.	$3.7\times {10}^4$
If the original number is: greater than 1, the power of 10 will be ${10}^n$ . between 0 and 1, the power of 10 will be ${10}^{\mathrm{-n}}$
Step 4 : Check.
${10}^4$ is 10,000 and 10,000 times 3.7 will be 37,000.
	$\mathrm{37,000}=3.7\times {10}^4$

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