1. Holt Algebra 1 11-1 Geometric Sequences Warm Up Find the value of each expression. 1. 2 5 2. 2 –5 3. –3 4 4. (–3) 4 32 5. (0.2) 3 6. 7(–4) 2 –81 81 112 0.008 7.8. 12(–0.4) 3 –0.768

2. Holt Algebra 1 11-1 Geometric Sequences Students will be able to: Recognize and extend geometric sequences and find the nth term of a geometric sequence. Learning Targets

3. Holt Algebra 1 11-1 Geometric Sequences The table shows the heights of a bungee jumper’s bounces. The height of the bounces shown in the table above form a geometric sequence. In a geometric sequence, the ratio of successive terms is the same number r, called the common ratio.

4. Holt Algebra 1 11-1 Geometric Sequences Example 1A: Extending Geometric Sequences Find the next three terms in the geometric sequence. 1, 4, 16, 64,… 5, –10, 20,–40,… 512, 384, 288,…

5. Holt Algebra 1 11-1 Geometric Sequences When the terms in a geometric sequence alternate between positive and negative, the value of r is negative. Helpful Hint The variable a is often used to represent terms in a sequence. The variable a 4 (read “a sub 4”)is the fourth term in a sequence. Writing Math

6. Holt Algebra 1 11-1 Geometric Sequences The variable a is often used to represent terms in a sequence. The variable a 4 (read “a sub 4”)is the fourth term in a sequence. Writing Math

7. Holt Algebra 1 11-1 Geometric Sequences Geometric sequences can be thought of as functions. The term number, or position in the sequence, is the input of the function, and the term itself is the output of the function. a 1 a 2 a 3 a 4 1 2 3 4 Position 3 6 12 24 Term To find the output a n of a geometric sequence when n is a large number, you need an equation, or function rule. Look for a pattern to find a function rule for the sequence above.

8. Holt Algebra 1 11-1 Geometric Sequences The pattern in the table shows that to get the nth term, multiply the first term by the common ratio raised to the power n – 1.

9. Holt Algebra 1 11-1 Geometric Sequences If the first term of a geometric sequence is a 1, the nth term is a n, and the common ratio is r, then an = a1rn–1an = a1rn–1 nth term1 st termCommon ratio

10. Holt Algebra 1 11-1 Geometric Sequences The first term of a geometric sequence is 500, and the common ratio is 0.2. What is the 7th term of the sequence? For a geometric sequence, a 1 = 5, and r = 2. Find the 6th term of the sequence? What is the 9th term of the geometric sequence 2, –6, 18, –54, …?

11. Holt Algebra 1 11-1 Geometric Sequences When writing a function rule for a sequence with a negative common ratio, remember to enclose r in parentheses. –2 12 ≠ (–2) 12 Caution

12. Holt Algebra 1 11-1 Geometric Sequences What is the 8th term of the sequence 1000, 500, 250, 125, …?

13. Holt Algebra 1 11-1 Geometric Sequences A ball is dropped from a tower. The table shows the heights of the balls bounces, which form a geometric sequence. What is the height of the 6th bounce? BounceHeight (cm) 1300 2150 375 HW pp. 769-771/8-40,42-46,54-62