2 Title

Beginning Algebra
Tutorial 29: Negative Exponents and Scientific Notation

Learning Objectives

 After completing this tutorial, you should be able to: Simplify exponential expressions involving negative exponents. Write a number in scientific notation. Write a number in standard notation, without exponents.

Introduction

 This tutorial picks up where Tutorial 26: Exponents left off.  It finishes the rules of exponents with negative exponents.  Also we will go over scientific notation. Like it or not, the best way to master these exponents is to work through exponent problems.  So I guess we better get to it.

Tutorial

 Negative Exponents    or

 Be careful with negative exponents.  The temptation is to negate the base, which would not be a correct thing to do. Since exponents are another way to write multiplication and the negative is in the exponent, to write it as a positive exponent we do the multiplicative inverse which is to take the reciprocal of the base.   Example 1:  Simplify .

 *Rewrite with a pos. exp. by taking recip. of base    *Use def. of exponents to evaluate

 Example 2:  Simplify .

 *Rewrite with a pos. exp. by taking recip. of base  *Use def. of exponents to evaluate

 Simplifying an Exponential Expression

 When simplifying an exponential expression,  write it so that each base is written one time with one POSITIVE exponent.  In other words, write it in the most condense form you can making sure that all your exponents are positive. A lot of times you are having to use more than one rule to get the job done.  As long as you are using the rule appropriately, you should be fine.

 Review of Exponent Rules

 Except for the negative exponent rule, examples of the following rules can be found in Tutorial 26: Exponents.   Product Rule:  Power Rule for Exponents:  Power of a Product:  Power of a Quotient:  Quotient Rule for Exponents:  Zero Exponent:  Negative Exponent:

 Example 3:    Simplify.  Write answer with positive exponents.

 Example 4:   Simplify.  Use positive exponents to write the answer.

 Example 5:   Simplify.  Use positive exponents to write the answer.

 Example 6:    Simplify.  Write answer with positive exponents.

 Be careful going into the last line.  Note that you do not see an exponent written with the number 5.  This means that the exponent on 5  is understood to be 1.  Since it doesn't have a negative exponent, we DO NOT take the reciprocal of 5.  The only base that has a negative exponent is a, so a is the only base we take the reciprocal of.

 Scientific Notation A positive number is written in scientific notation if it is written in the form: where 1 < a < 10 and r is an integer power of 10.

 Writing a Number in Scientific Notation

 Step 1:  Move the decimal point so that you have a number that is between 1 and 10.

 In other words, you will put your decimal after the first non zero number.

 Step 2:   Count the number of decimal places moved in Step 1 .

 If the decimal point was moved to the left, the count is positive. If the decimal point is moved to the right, the count is negative.

 Step 3:   Write as a product of the number (found in Step 1) and 10 raised to the power of the count (found in Step 2).

 Example 7:    Write the number in scientific notation:   483,000,000.

 *Decimal is at the end of the number *Move decimal to create a number between 1 and 10

 How many decimal places did we end up moving? We started at the end of the number 483000000 and moved it between the 4 and 8.  That looks like a move of 8 places. What direction did it move? Looks like we moved it to the left. So, our count is +8.

 Note how the number we started with is a bigger number than the one we are multiplying by in the scientific notation.  When that is the case, we will end up with a positive exponent

 Example 8:   Write the number in scientific notation:   .00054.

 *Decimal is at the beginning of the number *Move decimal to create a number between 1 and 10

 How many decimal places did we end up moving? We started at the beginning of the number .00054  moved it between the 5 and 4.  That looks like a move of 4 places. What direction did it move? Looks like we moved it to the right. So, our count is - 4.

 Note how the number we started with is a smaller number than the one we are multiplying by in the scientific notation.  When that is the case we will end up with a negative exponent.

 Write a Scientific Number in Standard Form

 Basically, you just multiply the first number times the power of 10.  Whenever you multiply by a power of 10, in essence what you are doing is moving your decimal place. If the power on 10 is positive, you move the decimal place that many units to the right. If the power on 10 is negative, you move the decimal place that many units to the left. Make sure you add in any zeros that are needed

 Example 9:  Write the number in standard notation, without exponents.

 *Move the decimal 6 to the right

 Example 10:  Write the number in standard notation, without exponents.

 *Move the decimal 5 to the left

Practice Problems

 These are practice problems to help bring you to the next level.  It will allow you to check and see if you have an understanding of these types of problems. Math works just like anything else, if you want to get good at it, then you need to practice it.  Even the best athletes and musicians had help along the way and lots of practice, practice, practice, to get good at their sport or instrument.  In fact there is no such thing as too much practice. To get the most out of these, you should work the problem out on your own and then check your answer by clicking on the link for the answer/discussion for that  problem.  At the link you will find the answer as well as any steps that went into finding that answer.

Practice Problems 1a - 1b: Simplify, use positive exponents to write each answer.

Practice Problem 2a: Write the number in scientific notation.

Practice Problem 3a: Write the number in standard notation, without exponents.

Need Extra Help on these Topics?

The following are webpages that can assist you in the topics that were covered on this page:

 http://www.sosmath.com/algebra/logs/log3/log32/log32.html This webpage helps with the quotient rule for exponents. http://www.purplemath.com/modules/exponent.htm This webpage gives an overall review of exponents.  It contains rules from both this tutorial and Tutorial 26: Exponents.

Go to Get Help Outside the Classroom found in Tutorial 1: How to Succeed in a Math Class for some more suggestions.

Last revised on August 2, 2011 by Kim Seward.