If (a_n=2n^2+2n+1), what are the first three terms?
Answer and explanation
Correct answer: (5, 13, 25)
Substitute n=1, 2, and 3 to obtain the first three terms. a₁=2(1)²+2(1)+1=5, a₂=2(2)²+2(2)+1=13, and a₃=2(3)²+2(3)+1=25. Hence, the correct sequence is (5, 13, 25). Option C has the correct first term, but for n=2 the value is 13, not 11. Exam tip: evaluate the squared term first and substitute each value of n separately.
Frequently asked questions
What is the correct answer to this question?
(5, 13, 25)
Why is this the correct answer?
Substitute n=1, 2, and 3 to obtain the first three terms. a₁=2(1)²+2(1)+1=5, a₂=2(2)²+2(2)+1=13, and a₃=2(3)²+2(3)+1=25. Hence, the correct sequence is (5, 13, 25). Option C has the correct first term, but for n=2 the value is 13, not 11. Exam tip: evaluate the squared term first and substitute each value of n separately.
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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