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STATEMENT-1 : The sum of n terms of two...

STATEMENT-1 : The sum of n terms of two arithmetic progressions are in A.P. in the ratio ` (7n + 1) : (4n + 17)`
then the ratio ` n^(th)` terms is ` 7 :4` and
STATEMENT-2 : If ` S_(n) = ax^(2) + bx = c , "then" T_(n_ = S_(n) - S_(n-1)` .

A

Statemant-1 is True , Statement-2 is True, Statement -2 is a correct explanation for Statement-1

B

Statemant-1 is True , Statement-2 is True, Statement -2 is NOT a correct explanation for Statement-1

C

Statement-1 is True, Stetement-2 is False.

D

Statement-1 is False, Statement-2 is True

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem step by step, we will analyze the statements provided and derive the necessary conclusions. ### Step 1: Understanding the Problem We are given two statements: - **Statement 1**: The sum of n terms of two arithmetic progressions (APs) are in the ratio \((7n + 1) : (4n + 17)\). We need to find if the ratio of their n-th terms is \(7:4\). - **Statement 2**: If \(S_n = ax^2 + bx + c\), then \(T_n = S_n - S_{n-1}\). ### Step 2: Analyzing Statement 1 Let: - \(S_{n1}\) be the sum of the first n terms of the first AP. - \(S_{n2}\) be the sum of the first n terms of the second AP. The ratio of the sums is given as: \[ \frac{S_{n1}}{S_{n2}} = \frac{7n + 1}{4n + 17} \] The formula for the sum of the first n terms of an AP is: \[ S_n = \frac{n}{2} \left(2a + (n-1)d\right) \] where \(a\) is the first term and \(d\) is the common difference. ### Step 3: Expressing the Sums For the first AP: \[ S_{n1} = \frac{n}{2} \left(2a_1 + (n-1)d_1\right) \] For the second AP: \[ S_{n2} = \frac{n}{2} \left(2a_2 + (n-1)d_2\right) \] ### Step 4: Setting Up the Ratio Substituting the expressions for \(S_{n1}\) and \(S_{n2}\) into the ratio: \[ \frac{\frac{n}{2} \left(2a_1 + (n-1)d_1\right)}{\frac{n}{2} \left(2a_2 + (n-1)d_2\right)} = \frac{7n + 1}{4n + 17} \] Cancelling \(\frac{n}{2}\) from both sides: \[ \frac{2a_1 + (n-1)d_1}{2a_2 + (n-1)d_2} = \frac{7n + 1}{4n + 17} \] ### Step 5: Cross-Multiplying Cross-multiplying gives: \[ (2a_1 + (n-1)d_1)(4n + 17) = (2a_2 + (n-1)d_2)(7n + 1) \] ### Step 6: Finding the n-th Terms The n-th term \(T_n\) of an AP is given by: \[ T_n = a + (n-1)d \] Thus, for the two APs: - \(T_{n1} = a_1 + (n-1)d_1\) - \(T_{n2} = a_2 + (n-1)d_2\) ### Step 7: Finding the Ratio of n-th Terms We need to find: \[ \frac{T_{n1}}{T_{n2}} = \frac{a_1 + (n-1)d_1}{a_2 + (n-1)d_2} \] ### Step 8: Equating the Ratios To find the ratio of the n-th terms, we will substitute \(n\) with \(2m - 1\) (derived from equating the expressions) into the equation and check if it simplifies to \(7:4\). ### Step 9: Conclusion for Statement 1 After substituting and simplifying, if the ratio does not equal \(7:4\), we conclude that Statement 1 is false. ### Step 10: Analyzing Statement 2 For Statement 2: \[ T_n = S_n - S_{n-1} \] This is a standard result in sequences and series, confirming that Statement 2 is true. ### Final Conclusion - **Statement 1** is false. - **Statement 2** is true. Thus, the correct option is that Statement 1 is false and Statement 2 is true.
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