Question

The 7th term of an AP is -4 and its 13th term is -16. Find the AP.

Answer 1

Let us say a be the first term and d be the common difference of an AP

a_n = a + (n – 1)d

a₇ = a + (7 – 1)d

= a + 6d = -4 …………(1)

And a₁₃ = a + 12d = -16 …..…..(2)

Subtracting equation (1) from (2), we get

6d = -16 – (-4) = -12

From (1), a + 6d = -4

a + (-12) = -4

a = -4 + 12 = 8

a = 8, d = -2

AP will be 8, 6, 4, 2, 0, ……