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# Check it out! - PowerPoint PPT Presentation

Check it out!. Sophia has a greenhouse. She’s trying to grow a demanding species of orchid that requires water every 3 days—no more, no less. The first day Sophia waters the orchids is Sunday, May 1. Use this information to answer the questions.

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Presentation Transcript

3.2.1: Sequences As Functions

Sophia has a greenhouse. She’s trying to grow a demanding species of orchid that requires water every 3 days—no more, no less. The first day Sophia waters the orchids is Sunday, May 1. Use this information to answer the questions.

3.2.1: Sequences As Functions

What is the fifth date on which Sophia will need to water the orchids?

What is the seventh date on which Sophia will need to water the orchids?

3.2.1: Sequences As Functions

Set up a calendar using what we know to find the date.

The first day Sophia waters the orchids is May 1. Fill in the calendar with this information.

3.2.1: Sequences As Functions

The problem tells us that Sophia waters the orchids every three days. Three days from May 1 is Wednesday, May 4, so the second time Sophia waters is May 4. Three days after May 4 is May 7.

3.2.1: Sequences As Functions

The third time Sophia waters the orchids is May 7. How can we use this information to find the fifth and seventh dates? What connection can we make between the third instance of watering and the date being May 7?

From the calendar, we see that at each instance of watering, the date has increased by 3 days. The first watering day is on May 1, the second is on May 4, and the third is on May 7. So we can say the number associated with the date should be 3 times the number associated with the instance of watering, or 3n, where n is the nth time Sophia needs to water the orchids.

3.2.1: Sequences As Functions

Check the formula by substituting values for we use this information to find the fifth and seventh dates? What connection can we make between the third instance of watering and the date being May 7?n. Use 1, 2, and 3 for the first, second, and third times Sophia waters the orchids.

3n = x

3(1) = 3 = May 3

3(2) = 6 = May 6

3(3) = 9 = May 9

3.2.1: Sequences As Functions

These dates don’t match what we see on the calendar. We need to adjust our formula so that the first watering is on May 1.

If we subtract 2 from 3n, we get the following:

3n – 2 = x

3(1) – 2 = 1 = May 1

3(2) – 2 = 4 = May 4

3(3) – 2 = 7 = May 7

The formula 3n – 2 = x, where n is the nth watering and x is the date, is correct for the first, second, and third times Sophia needs to water the orchids.

3.2.1: Sequences As Functions

Substitute 5 into the formula 3n – 2 = x.

3n – 2 = x

3(5) – 2 = 15 – 2 = 13

The fifth time Sophia needs to water the orchids is on May 13. Check this using the calendar.

We need to expand our calendar table for another week.

Add a week to the calendar and fill it out to check what we’ve found.

3.2.1: Sequences As Functions

3.2.1: Sequences As Functions

Substitute 7 into the formula 3n – 2 = x.

3n – 2 = x

3(7) – 2 = 21 – 2 = 19

The formula predicts that Sophia will water the plants on May 19. Add another week to the calendar and confirm.

3.2.1: Sequences As Functions

We see the formula 3 the orchids?n – 2 = x is able to predict the watering dates for Sophia.

The third, fifth, and seventh dates on which Sophia must water the orchids are May 7, May 13, and May 19.

3.2.1: Sequences As Functions