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If 9 times the 9th term of an A.P. is eq...

If 9 times the 9th term of an A.P. is equal to 13 times the 13 term, then the 22nd term of the A.P. is
(i) 0
(ii) 22
(iii) 220
(iv) 198

A

0

B

22

C

220

D

198

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to find the 22nd term of an arithmetic progression (A.P.) given that 9 times the 9th term is equal to 13 times the 13th term. ### Step-by-Step Solution: 1. **Define the terms of the A.P.**: Let \( A \) be the first term and \( D \) be the common difference of the A.P. The formula for the \( n \)-th term of an A.P. is given by: \[ A_n = A + (n - 1)D \] 2. **Write expressions for the 9th and 13th terms**: - The 9th term \( A_9 \) is: \[ A_9 = A + 8D \] - The 13th term \( A_{13} \) is: \[ A_{13} = A + 12D \] 3. **Set up the equation based on the given condition**: According to the problem, we have: \[ 9 \cdot A_9 = 13 \cdot A_{13} \] Substituting the expressions for \( A_9 \) and \( A_{13} \): \[ 9(A + 8D) = 13(A + 12D) \] 4. **Expand both sides**: Expanding the left side: \[ 9A + 72D \] Expanding the right side: \[ 13A + 156D \] 5. **Set the equation**: Now we can set the two sides equal to each other: \[ 9A + 72D = 13A + 156D \] 6. **Rearrange the equation**: Rearranging gives: \[ 9A - 13A + 72D - 156D = 0 \] Simplifying this leads to: \[ -4A - 84D = 0 \] 7. **Factor out common terms**: Dividing the entire equation by -4 gives: \[ A + 21D = 0 \] 8. **Interpret the result**: The expression \( A + 21D = 0 \) indicates that the 22nd term \( A_{22} \) can be expressed as: \[ A_{22} = A + 21D \] Since \( A + 21D = 0 \), we have: \[ A_{22} = 0 \] ### Conclusion: Thus, the 22nd term of the A.P. is \( 0 \). ### Final Answer: The answer is (i) 0.
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