Question

If 10 times the 10^th term of an A.P. is equal to 15 times the 15^th term, show that 25^th term of the A.P. is zero.

Answer 1

10a₁₀ = 15a₁₅

10[a + (10 – 1)d] = 15[a + (15 – 1)d]

2a + 2(9)d = 3a + 3(14)d

- a = 42d – 18d

- a = 24d

a = - 24d

a₂₅ = a + 24d

= - 24d + 24d

= 0