Question

In an AP if the common difference (d) = - 4, and the seventh term (a₇) is 4, then find the first term.

Answer 1

Given d = -4 and a₇ =  4

We know that n^th  terrn of A.P is

a_{n =} a +(n-1) d

a₇ =  a +  (7 -1)d  [ n = 7 ] 

4 = a + 6 (-4)

.'.    a = 4 + 24 = 28

.'.  First term of an A.P = 28