Mathematics
Find the 15th term of the A.P. with second term 11 and common difference 9.
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Answer
We know that,
⇒ an = a + (n - 1)d
⇒ a2 = a + (2 - 1)d
⇒ 11 = a + d
⇒ 11 = a + 9
⇒ a = 11 - 9 = 2.
a15 = a + (15 - 1)d
= 2 + 14 × 9
= 2 + 126
= 128.
Hence, 15th term = 128.
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