2. Yesterday, we generated the formula for the sum of an arithmetic sequence. Today, we will use the same approach to determine the formula for the sum of a geometric sequence.

3. Determine the sum of the Geometric Sequence 2 + 4 + 8 + 16 =30 Develop an algebraic method S = 2 + 4 + 8 + 16 2S = 0 + 4 + 8 + 16 + 322S = 4 + 8 + 16 + 32 S = 2 + 4 + 8 + 16 + 0 -2 + 0 + 0 + 0 +32= 30

4. Similar to an Arithmetic Sequence, these ideas can be extended to a general formula Sum of a Geometric Series S n = a(r n –1) r - 1

5. S 4 = 2(2 4 – 1) 2 – 1 = 2(15) 1 = 30 Determine the sum of the GS 2 + 4 + 8 + 16 =30 a = 2, r = 2, n = 4

6. S 10 = 24[(-0.5) 10 – 1] -0.5 – 1 = 24(-0.999) -1.5 = 15.984 Determine the sum of the first 10 terms of the GS 24 – 12 + 6 – 3 + … a = 24, r = -0.5, n = 10

7. Remember: If you are not given the number of terms (n), you can use the term formula to find it!!!

8. Pg 476 [1-3]a,c,e 7,10,12