Question

An ap consist of 21 terms the sum of 3terms in the middle is 129 and of the last 3 is 237 find ap

Answer 1

Answer:

Step-by-step explanation:

First term a =3

common difference d= 4.

Solution:

In an AP, nth term is given as Tn = a+ (n-1)d

n = 21

sum of last three terms i.e. T19, T20, T21

sum of three middle terms T10,T11 and T12

Subtract both equations

Put the value of d, into eq 1 or eq2

So ,First term a =3

common difference d= 4.