Question

The 4+a term of an Ap is zero prove the 25th term of the Ap is three times its 11th term

Answer 1

Given a4 = 0

That is (a + 3d) = 0

⇒ a = - 3d → (1)

nth term of AP is given by an = a + (n – 1)d

a11 = a + 10d = – 3d + 10d = 7d  [From (1)]

a25 = a+ 24d = – 3d + 24d = 21d  [From (1)]

      = 3 x 7d

Hence a25 = 3 x a11