Which option gives the first four terms of (a_n=n(n+2))?
Answer and explanation
Correct answer: (3, 8, 15, 24)
The rule is a_n=n(n+2). Substituting n=1 gives 1(1+2)=3; n=2 gives 2(2+2)=8; n=3 gives 3(3+2)=15; and n=4 gives 4(4+2)=24. Therefore, the first four terms are (3, 8, 15, 24), so option C is correct. Option A begins with 2, but the correct first term for n=1 must be 3. Exam tip: For a general-term question, substitute n=1, 2, 3, and so on in order.
Frequently asked questions
What is the correct answer to this question?
(3, 8, 15, 24)
Why is this the correct answer?
The rule is a_n=n(n+2). Substituting n=1 gives 1(1+2)=3; n=2 gives 2(2+2)=8; n=3 gives 3(3+2)=15; and n=4 gives 4(4+2)=24. Therefore, the first four terms are (3, 8, 15, 24), so option C is correct. Option A begins with 2, but the correct first term for n=1 must be 3. Exam tip: For a general-term question, substitute n=1, 2, 3, and so on in order.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Explicit or general rule.
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