1.4.3 Sum of the First n Terms of a Geometric Progression

1.4.3 Sum of the First n Terms of Geometric Progressions

(F) Sum of the First Terms of Geometric Progressions
S n = a ( r n 1 ) r 1 , r > 1 S n = a ( 1 r n ) 1 r , r < 1 a = first term
r = common ratio
n = number of term
Sn = sum of the first n terms

Example 1:
Find the sum of each of the following geometric progressions.
(a) 1, 2, 4, …  up to the first 7 terms
(b) 9, 3,   1,   ,   …    up to the first 6 terms
(c) 12, 3, …., 3 64 [Smart TIPS: You can find n if you know the last term]




Solution:







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