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