Find
the sum of the 1st 20 terms of the following arithmetic progression:
5+11+17+…………………
Solution
d=6,
A1 = 5,n=16
Sn
= n[2A1 + (n-1)d]
2
S20
= 20[2(5) + (20-1)d]
2
S20
= 10[10 + 19d]
S20
= 8[10 + 19(6)] since d=6
S20
= 8[10 + 114]
S20
= 8 x 124
S20
= 992
Therefore the sum of 1st 20 terms is 992.
TRY THIS......
Find
the sum of the 1st 22 terms of the following arithmetic progression:
6+14+22+…………………
No comments:
Post a Comment