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# Find the Sum of the First 15 Terms of Each of the Following Sequences Having the Nth Term as Bn = 5 + 2n - CBSE Class 10 - Mathematics

ConceptSum of First n Terms of an AP

#### Question

Find the sum of the first 15 terms of each of the following sequences having the nth term as

bn = 5 + 2n

#### Solution

Here, we are given an A.P. whose nth term is given by the following expression

We need bn = 5 + 2n to find the sum of first 15 terms.

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

S_n = (n/2)(a + l)

Where a = the first term

l = the last term

So, for the given A.P,

The first term (a) will be calculated using n = 1inthe given equation for the nth term of A.P

b = 5 + 2(1)

=- 5 + 2

= 7

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

l = b_n = 5 + 2n

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

S_15 = (15/2)[(7) + 5 + 2(15)]

=(15/2)[12 + 30]

= (15/2)(42)

= (15)(21)

= 315

Therefore, the sum of the 15 terms of the given A.P. is S_15 = 315

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Solution Find the Sum of the First 15 Terms of Each of the Following Sequences Having the Nth Term as Bn = 5 + 2n Concept: Sum of First n Terms of an AP.
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