Question

 If the common difference of an A.P. is – 3 and the 18th term is – 5, then find its first term.

Answer 1

Common difference (d) = -3
T₁₈ = -5
a + (n – 1 )d = Tn
a + (18 – 1) (-3) = -5
⇒ a + 17(–3) = –5
⇒ a – 51 = –5
⇒ a = –5 + 51 = 46
∴ First term = 46.