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Given p A.P's , each of which consists ...

Given p A.P's , each of which consists on n terms . If their first terms are `1,2,3……` p and common differences are `1,3,5,……,2p-1 ` respectively , then sum of the terms of all the progressions is

A

`1/ 2 np(np+1)`

B

`1/2 n(p+1)`

C

`np(n+1)`

D

none of these

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem step by step, we will find the sum of the terms of all the given arithmetic progressions (APs). ### Step 1: Identify the first terms and common differences of the APs The first terms of the p APs are: - 1, 2, 3, ..., p The common differences of the p APs are: - 1, 3, 5, ..., (2p - 1) ### Step 2: Calculate the sum of the first terms The sum of the first terms can be calculated using the formula for the sum of the first n natural numbers: \[ S_A = \sum_{k=1}^{p} k = \frac{p(p + 1)}{2} \] ### Step 3: Calculate the sum of the common differences The common differences form an arithmetic progression where: - First term (A) = 1 - Common difference (d) = 2 - Number of terms (n) = p The last term of this AP is \(2p - 1\). The sum of the first p odd numbers can also be calculated as: \[ S_D = \sum_{k=1}^{p} (2k - 1) = p^2 \] ### Step 4: Calculate the sum of the terms of each AP The sum of the terms of an AP is given by the formula: \[ S_n = \frac{n}{2} \left(2A + (n - 1)d\right) \] For each AP, we have: - \(A\) as the first term (1, 2, 3, ..., p) - \(d\) as the common difference (1, 3, 5, ..., (2p - 1)) - \(n\) as the number of terms (n) Thus, for each AP, the sum becomes: \[ S_{AP} = \frac{n}{2} \left(2k + (n - 1)(2k - 1)\right) \] where \(k\) is the first term of the respective AP. ### Step 5: Substitute the values into the sum formula Substituting the values of \(A\) and \(d\): \[ S_{AP} = \frac{n}{2} \left(2k + (n - 1)(2k - 1)\right) \] This simplifies to: \[ S_{AP} = \frac{n}{2} \left(2k + (n - 1)(2k) - (n - 1)\right) \] \[ = \frac{n}{2} \left(n \cdot 2k - (n - 1) + 2k\right) \] \[ = \frac{n}{2} \left( (n + 1) \cdot 2k - (n - 1) \right) \] ### Step 6: Total sum of all APs Now, we need to sum \(S_{AP}\) for all \(k\) from 1 to \(p\): \[ S_{total} = \sum_{k=1}^{p} S_{AP} \] \[ = \sum_{k=1}^{p} \frac{n}{2} \left( (n + 1) \cdot 2k - (n - 1) \right) \] This can be simplified to: \[ = \frac{n}{2} \left( (n + 1) \cdot \sum_{k=1}^{p} 2k - p(n - 1) \right) \] Using the sum of the first \(p\) natural numbers: \[ = \frac{n}{2} \left( (n + 1) \cdot p(p + 1) - p(n - 1) \right) \] ### Final Result Thus, the total sum of the terms of all the progressions is: \[ = \frac{np}{2} \left( nP + 1 \right) \]
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