If the sum of n terms of an A.P. is 3n2 + 5n and its mth term is 164, find the value of m.
Therefore, from (1), we obtain
8 + (m – 1) 6 = 164
⇒ (m – 1) 6 = 164 – 8 = 156
⇒ m – 1 = 26
⇒ m = 27
Thus, the value of m is 27..
Answer
Let a and b be the first term and the common difference of the A.P. respectively.
am = a + (m – 1)d = 164 … (1)
am = a + (m – 1)d = 164 … (1)
Therefore, from (1), we obtain
8 + (m – 1) 6 = 164
⇒ (m – 1) 6 = 164 – 8 = 156
⇒ m – 1 = 26
⇒ m = 27
Thus, the value of m is 27..
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