Question 1 Report
The seconds term of a geometric series is 4 while the fourth term is 16. Find the sum of the first five terms
Answer Details
T2 = 4, T4 = 16 Tx = arn-1 T2 = ar2-1 = 4 i.e. ar3 = 16, i.e. ar = 4 T4 = ar4-1 therefore, T4Tr T 4 T r = ar3ar a r 3 a r = 164 16 4 r2 = 4 and r = 2 but ar = 4 a = 4r 4 r = 42 4 2 a = 2 Sn = a(rn−1)r−1 a ( r n − 1 ) r − 1 S5 = 2(25−1)2−1 2 ( 2 5 − 1 ) 2 − 1 = 2(32−1)2−1 2 ( 32 − 1 ) 2 − 1 = 2(31) = 62