Question

If a nad 1 are first and last term of apthen the no of terms are

Answer 1

If a and l be the first and last term of an A.P. and S be the sum of  its all terms, then its common difference is-

A

2S−l−al2+a2

B

2S−l−al2−a2

C

2S−l+al2−a2

D

Solution



Let S be the sum of  its all terms

S=2n(a+l)

⇒2S=n(a+l)

⇒n=a+l2S

If a and l be the first and last term of an A.P.then

l=a+(n−1)d

⇒l−a=(n−1)d

⇒d=n−1l−a

⇒d=a+l2S