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.
Determine the sum of the Geometric Sequence =30 Develop an algebraic method S = S = S = S = = 30
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
S 4 = 2(2 4 – 1) 2 – 1 = 2(15) 1 = 30 Determine the sum of the GS =30 a = 2, r = 2, n = 4
S 10 = 24[(-0.5) 10 – 1] -0.5 – 1 = 24(-0.999) -1.5 = Determine the sum of the first 10 terms of the GS 24 – – 3 + … a = 24, r = -0.5, n = 10
Remember: If you are not given the number of terms (n), you can use the term formula to find it!!!
Pg 476 [1-3]a,c,e 7,10,12