If (a_n=7n-4), what is (a_{3m})?
Answer and explanation
Correct answer: \(21m-4\)
Given \(a_n=7n-4\), substitute \(3m\) for \(n\): \(a_{3m}=7(3m)-4=21m-4\). Hence, the correct answer is \(21m-4\). The expression \(21m-12\) incorrectly multiplies the constant \(-4\) by 3. Exam tip: when the index changes, replace only \(n\) throughout the formula and do not alter a constant term unnecessarily.
Frequently asked questions
What is the correct answer to this question?
\(21m-4\)
Why is this the correct answer?
Given \(a_n=7n-4\), substitute \(3m\) for \(n\): \(a_{3m}=7(3m)-4=21m-4\). Hence, the correct answer is \(21m-4\). The expression \(21m-12\) incorrectly multiplies the constant \(-4\) by 3. Exam tip: when the index changes, replace only \(n\) throughout the formula and do not alter a constant term unnecessarily.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: nth term.
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