If (a_1=4) and (a_{n+1}=a_n+2n+1), what is the value of (a_7)?
Answer and explanation
Correct answer: 52
Substituting n=1,2,3,4,5,6 successively in the recurrence gives a_2=7, a_3=12, a_4=19, a_5=28, a_6=39, and a_7=52. Hence, the correct answer is 52. A value such as 50 can result from adding an incorrect increment instead of 2n+1 at one step. Exam tip: for each new term, use the index of the preceding term as n.
Frequently asked questions
What is the correct answer to this question?
52
Why is this the correct answer?
Substituting n=1,2,3,4,5,6 successively in the recurrence gives a_2=7, a_3=12, a_4=19, a_5=28, a_6=39, and a_7=52. Hence, the correct answer is 52. A value such as 50 can result from adding an incorrect increment instead of 2n+1 at one step. Exam tip: for each new term, use the index of the preceding term as n.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Sequences.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
