If (a_n=3n^2+n-2), what is the sum of the first three terms?
Answer and explanation
Correct answer: 42
Using a_n=3n^2+n-2: a_1=3(1)^2+1-2=2, a_2=3(2)^2+2-2=12, and a_3=3(3)^2+3-2=28. Therefore, the sum of the first three terms is 2+12+28=42. Option 40 is incorrect because the third term is 28, not 26. Exam tip: substitute each value of n separately before adding the terms.
Frequently asked questions
What is the correct answer to this question?
42
Why is this the correct answer?
Using a_n=3n^2+n-2: a_1=3(1)^2+1-2=2, a_2=3(2)^2+2-2=12, and a_3=3(3)^2+3-2=28. Therefore, the sum of the first three terms is 2+12+28=42. Option 40 is incorrect because the third term is 28, not 26. Exam tip: substitute each value of n separately before adding the terms.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Explicit or general rule.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
