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3.05 The laws of exponents and scientific notation

Lesson

We've previously looked at how to use scientific notation to write really big or really small numbers. Remember they are written in the form $a\times10^b$a×10b, where $1\le a<10$1a<10 and $b$b is an integer. Since these numbers are all written in relation to a power of $10$10, we can simplify expressions written in scientific notation using the laws of exponents, such as the product of powers property or the quotient of powers property.

 

Adding and subtracting using scientific notation

If you are adding or subtracting numbers written in scientific notation, you need to make sure that the powers of ten are the same. To do this, you may need to factor some of the powers of $10$10 based on the product of powers property. Then you can use the decimal number, rather than the number in scientific notation and evaluate the problem. The process goes:

$a\times10^n\pm b\times10^m$a×10n±b×10m $=$= $a\times10^n\pm b\times10^{m-n}\times10^n$a×10n±b×10mn×10n
  $=$= $\left(a\pm b\times10^{m-n}\right)\times10^n$(a±b×10mn)×10n

 

Multiplying and dividing using scientific notation

If you are multiplying or dividing numbers written in scientific notation, we will use the commutative property to multiply or divide the powers of $10$10 by one another and then the  "$a$a" values by one another. 

$\left(a\times10^m\right)\left(b\times10^n\right)$(a×10m)(b×10n) $=$= $\left(a\times b\right)\left(10^m\times10^n\right)$(a×b)(10m×10n)
  $=$= $\left(a\times b\right)\times10^{m+n}$(a×b)×10m+n
$\frac{a\times10^m}{b\times10^n}$a×10mb×10n $=$= $\frac{a}{b}\times\frac{10^m}{10^n}$ab×10m10n
  $=$= $\frac{a}{b}\times10^{m-n}$ab×10mn

 

Powers of numbers in scientific notation

Recall the power of a power and power of a product properties. We will use both properties to take a raise a number in scientific notation to a power. The process goes:

$\left(a\times10^m\right)^n$(a×10m)n $=$= $a^n\times\left(10^m\right)^n$an×(10m)n
  $=$= $a^n\times10^{mn}$an×10mn
Tip

Make sure you check that your final answer is expressed appropriately in scientific notation. Simplify as required.

Worked example

Question 1

Use the laws of exponents to simplify $\left(2\times10^6\right)\times\left(6\times10^5\right)$(2×106)×(6×105). Give your answer in scientific notation.

Think: Let's simplify the expression first. Remember to express our answer in scientific notation, we'll need to express the coefficient as a value between $1$1 and $10$10 and then multiply it by the correct power of $10$10.

Do:

$2\times10^6\times6\times10^5$2×106×6×105 $=$= $\left(2\times6\right)\times\left(10^6\times10^5\right)$(2×6)×(106×105)
  $=$= $12\times10^{6+5}$12×106+5
  $=$= $12\times10^{11}$12×1011

$12$12 can be as expressed as $1.2\times10^1$1.2×101. We will use this to write our answer in scientific notation.

$1.2\times10^1\times10^{11}$1.2×101×1011 $=$= $1.2\times10^{1+11}$1.2×101+11
  $=$= $1.2\times10^{12}$1.2×1012

Reflect: How might you summarize the steps above to a classmate?

 

Practice questions

Question 2

Use exponent laws to simplify $\frac{3\times10^3}{12\times10^{-1}}$3×10312×101. Give your answer in scientific notation.

Question 3

Evaluate $1.77\times10^9+3.24\times10^{10}$1.77×109+3.24×1010.

Give your answer in scientific notation to three significant figures.

 

Outcomes

8.NS.3

Given a numeric expression with common rational number bases and integer exponents, apply the properties of exponents to generate equivalent expressions

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