Question

the first and last term of an AP are 4 and 18 respectively.It the common difference is 7,how many terms are there in the AP and what is their sum​

Answer 1

Answer:

S=

2

n

(a+l) or

a+l

2S

=n ..(1)

l=a+(n−1)d so that d=

n−1

l−a

.(2)

Now put for n from (1) in (2),then we get

d =

2S−(l+a)

l

2

−a

2