Question

If the nth term of an A.P. is (2n + 1), then the sum of its first three terms is
O 18
O 15
h
O 12
O 21
DES
0​

Answer 1

nth term = a+(n-1)d
(2n+1)= a+ nd -d
By comparison, we get
d=2 and a=3
Therefore the first 3 terms of the ap are 3, 5, 7. Sum of the terms is 15