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Question
If the sum of n terms of an A.P. be 3n2 + n and its common difference is 6, then its first term is ______.
Options
2
3
1
4
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Solution
If the sum of n terms of an A.P. be 3n2 + n and its common difference is 6, then its first term is 4.
Explanation:
In the given problem, the sum of n terms of an A.P. is given by the expression,
Sn = 3n2 + n
Here, we can find the first term by substituting n = 1 as sum of first term of the A.P. will be the same as the first term. So we get,
Sn = 3n2 + n
S1 = 3 (1)2 + (1)
= 3 + 1
= 4
Therefore, the first term of this A.P is a = 4.
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