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If (a_n=2n^2-kn) and (a_4=24), what is the value of (k)?
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Answer and explanation
Correct answer: 2
Given (a_n=2n^2-kn), substitute n=4: (a_4=2(4)^2-4k=32-4k). Since (a_4=24), we get (32-4k=24), so (4k=8) and hence (k=2). Therefore, option C is correct. If k=3, then (a_4=20), not 24. Exam tip: When a particular term is given, substitute that term number for n first.
Frequently asked questions
What is the correct answer to this question?
2
Why is this the correct answer?
Given (a_n=2n^2-kn), substitute n=4: (a_4=2(4)^2-4k=32-4k). Since (a_4=24), we get (32-4k=24), so (4k=8) and hence (k=2). Therefore, option C is correct. If k=3, then (a_4=20), not 24. Exam tip: When a particular term is given, substitute that term number for n first.
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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