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Lesson 6.5: Looking Back with Exponents

Lesson 6.5: Looking Back with Exponents. To review or learn the division property of exponents. In the previous lesson you learned that looking ahead in time to predict future growth with an exponential model is related to the multiplication property of exponents.

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Lesson 6.5: Looking Back with Exponents

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  1. Lesson 6.5: Looking Back with Exponents To review or learn the division property of exponents

  2. In the previous lesson you learned that looking ahead in time to predict future growth with an exponential model is related to the multiplication property of exponents. • In this lesson you’ll discover a rule for dividing expressions with exponents. Then you’ll see how dividing expressions is like looking back in time.

  3. The Division Property of Exponents • Step 1: • Write the numerator and the denominator of each quotient in expanded form. • Then reduce to eliminate common factors. • Rewrite the factors that remain with exponents. Use your calculator to check your answers.

  4. Step 2: • Compare the exponents in each final expression you got in Step 1 to the exponents in the original quotient. • Describe a way to find the exponents in the final expression without using expanded form.

  5. Step 3: • Use your method from Step 2 to rewrite this expression so that it is not a fraction. You can leave as a fraction.

  6. Recall that exponential growth is related to repeated multiplication. When you look ahead in time you multiply by repeated constant multiplication, or increase the exponent. • To look back in time you will need to undo some of the constant multipliers, or divide.

  7. Step 4 • Apply what you have discovered about dividing expressions with exponents. • After 7 years the balance in a saving account is 500(1+0.04)7. What does the expression mean in this situation? • Rewrite this expression with a single exponent. The balance 3 years prior.

  8. After 9 years of depreciation, the value of a car is , • What does the expression mean in this situation? • Rewrite this expression with a single exponent. The balance 5 years prior

  9. After 5 weeks the population of a bug colony is 32(1+0.50)5. • Write a division expression to show the population 2 weeks earlier. • Rewrite your expression with a single exponent.

  10. The expression A(1+r)n can model n time periods of exponential growth. What expression models the growth m time periods earlier.

  11. Step 5 • How does looking back in time with an exponential model relate to dividing expressions with exponents? Dividing by (1+r)m represents looking back m time periods.

  12. Expanded form helps you understand many properties of exponents. It also helps you understand how the properties work together.

  13. Example A • Use the properties of exponents to rewrite each expression.

  14. For any non-zero value of b and any integer value of m and n

  15. Example B • Six years ago, Anne bought a van for $18,500 for her flower delivery service. Based on the prices of similar used vans, she estimates a rate of depreciation of 9% per year. • How much is the van worth now? • How much was the van worth last year? • How much was it worth 2 years ago?

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