Tuesday 6 December 2016

SUM OF AP 1


Find the sum of the 1st 18 terms of the following arithmetic progression: 5+11+17+…………………

Solution

d=6, A1 = 5,n=18

Sn = n[2A1 + (n-1)d]
       2

S18 = 18[2(5) + (18-1)d]
         2

S18 = 9[10 + 17d]
 
S18 = 9[10 + 17(6)]       since d=6

S18 = 9[10 + 102]  
         
S18 = 9 x 112 
          
S18 = 1008


Therefore the sum of 1st 18 terms is 1008.

TRY THIS............

Find the sum of the 1st 12 terms of the following arithmetic progression: 6+10+14+…………………


No comments:

Post a Comment