Question

Arithmetic sequence help!!!!

Answer 1

1) This is not an arithmetic sequence because it has n².

2) To find 5 first terms of this sequence, you can simply substitute n with 1,2,3,4, and 5, and calculate values of a(1),a(2), a(3), a(4) and a(5).

a(n) = 3n²- 1

n=1 a=3*1² - 1 = 3-1=2

n=2 a=3*2² - 1 = 11

n=3 a=3*3² - 1 =26

n=4 a=3*4² - 1 = 47

n=5 a=3*5² -1 = 74

2,11,26,47,74

Answer C. 2,11,26,47,74.

Answer 2

Remark: All you can do is put numbers in until you find something that gives you the right sequence by eliminating all the other choices.

Solution: All of them say that the first term is 2. That almost tells us nothing. However there is one thing you do learn. n's first value must be 1. How do you know it is not 0? 3*(1)^2 = 3*1 = 3; when you subtract 1 from 3 you get two. So the first value for n = 1

What happens when n = 2? 3*2^2 = 3*4 = 12. That means that 3*n^2 - 1 = 11.

D is not the answer.

Now let n = 3.

3*3^2 - 1

3 * 9 - 1 = 27 - 1 = 26

The third term must be 26. That eliminates A and B

There is only one choice left: C is the answer.