Question

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

Answer 1

Answer:

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.

Hope it helps you
¶¶¶♀♂♀♂
✌✌✌