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Question

If the nth term of an A.P. is 2n + 1, then the sum of first n terms of the A.P. is

(a) n(n − 2)

(b) n(n + 2)

(c) n(n + 1)

(d) n(n − 1)

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Solution

Here, we are given an A.P. whose nth term is given by the following expression, . We need to find the sum of first n terms.

So, here we can find the sum of the n terms of the given A.P., using the formula,

Where, a = the first term

l = the last term

So, for the given A.P,

The first term (a) will be calculated using in the given equation for nth term of A.P.

Now, the last term (l) or the nth term is given

So, on substituting the values in the formula for the sum of n terms of an A.P., we get,

Therefore, the sum of the n terms of the given A.P. is. So the correct option is (b).


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