If the 2nd and 5th terms of a G.P are 6 and 48 respectively, find the sum of the first for term
-45
-15
15
33
45
Correct answer is E
T2 = ar = 6
T5 = ar4 = 48
T5T2 = ar4ar = 486
= r3 = 8
⇒ r = 2
Sn = a((rn)−1)r−1
S4 = a((r4)−1)r−1
S4 = 3((24)−1)2−1
= 3(16 -1)
= 45