Question

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

Answer 1

a + 6 (–4) = 4

⇒ a = 28

Detailed Answer :

Given d = – 4 and a₇ = 4

We know that nth term 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.

Answer 2

n th term a_n = a₁+ (n-1)d

a₇ = a₁+( 7-1)* (-4)

=> 4 = a₁+( 7-1)* (-4)

=> a₁= 4-+24 =28