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Learning Targets: I can use geometric sequences to model growth and decay. I can use recursion notation to model growth and decay. Introduction to growth & decay. REVIEW: arithmetic sequence u n = u n-1 + d d is the common difference geometric sequence u n = r ∙ u n-1
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Learning Targets: • I can use geometric sequences to model growth and decay. • I can use recursion notation to model growth and decay. Introduction to growth & decay
REVIEW: arithmetic sequenceun = un-1 + d d is the common difference geometric sequenceun = r ∙ un-1 r is the common ratio
Example: 308, 231, 173.25, 128.9375, 97.453125,… Arithmetic or geometric sequence? Common ratio? Growth or decay? By what percentage? Write recursive sequence: Find 10th term
Example: Jim deposits $200 in an account which gets 7% interest. Write a recursive sequence. U0 = 200 Why u0? And not u1? Un = 1.07 ∙ un-1 Why 1.07?
Growth = (100% + P) Decay = (100% - P) Important Note: write this as a decimal
What do the graphs of growth and decay look like?? The same amount is NOT being added or subtracted, so the graph is NOT linear. Growth Decay
Example: Suppose the initial height from which a rubber ball drops is 100 cm. The rebound heights to the nearest cm are 80, 64, 51, 41, … What is the rebound ratio for this ball? What is the height after the 10th bounce? After how many bounces will the ball be less than 1 cm?
Example: A book store is going out of business. They will mark their books down an additional 10% each week until they sell all of their inventory. If a book costs $35, how much will it cost after 4 weeks?
Example: U0=1000 Un=(1.3)un-1 Growth or decay? By what percentage? U0=222 Un=(0.3) un-1 Growth or decay? By what percentage?
Learning Targets: • I can use geometric sequences to model growth and decay. • I can use recursion notation to model growth and decay. More examples of Growth & Decay
Example: An automobile depreciates as it gets older. Suppose that a particular automobile loses 1/5 of its value each year. Write a recursive formula to find the value of this car when it is 6 years old if it costs $23,999 when it was new. u0=23,999 un=4/5(un-1) or un=.8*un-1 answer: after 6 years it is worth $6291.19
Carbon dating is used to find the age of ancient remains of once-living things. Carbon-14 is found naturally in all living things, and it decays slowly after death. About 11.45% of it decays every 1,000 years. Let 100% or 1 be the beginning amount of Carbon-14. At what point will less than 8% remain? Write a recursive formula you used. Answer: U0=1 Un=(1-.1145)un-1(or use .8855 in parenthesis) 22,00 years
Suppose $825 is deposited in an account that earns 7.5% annual interest and no more deposits or withdrawals are made. If the interest is compounded monthly, what is the monthly rate? (7.5%/12 months) = 0.625% = .00625 U0=825 Un=(1+.075/12)*un-1 What is the balance after 1 month? What is the balance after 1 year? What is the balance after 35 months?
Write a recursive formula for 115, 103, 91, 79,… Arithmetic or geometric? What term will give you the first negative number?
Assignment: page 41 10, 11, 12abc, 13, 18