Find the sum of the first 18 terms of the progr... - JAMB Mathematics 1990 Question
Find the sum of the first 18 terms of the progression 3, 6, 12......
A
3(217 - 1)
B
3(218 - 1)
C
3(218 + 1)
D
3(217 - 1)
correct option: d
3 + 6 + 12 + .....18thy term
1st term = 3, common ratio (\frac{6}{3}) = 2
n = 18, sum og GP is given by Sn = a(\frac{(r^n - 1)}{r - 1})
s18 = 3(\frac{(2^{18} - 1)}{2 - 1})
= 3(217 - 1)
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