Question

The first and last term of an A.P. are 1 and 13 respectively.If the sum of its n terms is 42 , then find n​

Answer 1

Step-by-step explanation:

a= 1

l =13

Sn =42

n=?

Sn = n/2(a+l)

42=n/2 (1+13)

42=n/2*14

n/2= 42/14

n/2=3

n=6