Given that the first and forth terms of G P are... - JAMB Mathematics 2004 Question
Given that the first and forth terms of G.P are 6 and 162 respectively, find the sum of the first three terms of the progression
A
27
B
8
C
78
D
48
correct option: c
\(a=6, U_4 = 162\U_4 = ar^{4-1}\U_4 = ar^3\162 = 6(r)^3\r^3 = 27\r=\sqrt[3]{27}\r=3\S_4 = \frac{a(r^{n}-1)}{r-1}\=\frac{6(3^{3}-1)}{3-1}\=\frac{6(27-1)}{2}\=3\times26\=78\)
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