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Question
In an AP, if the common difference (d) = –4, and the seventh term (a7) is 4, then find the first term.
Solution
nth term of an AP is Tn=a+(n−1)d
For an AP with the first term as 'a' and common difference as 'd', the seventh term is a + 6d.
According to the question, the common difference(d) is −4 and the seventh term(a7) is 4.
So, a + 6d will be
⇒ a + 6(−4) = 4
⇒ a = 28
Hence, the first term is 28.
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