Question

Part 1.] Indicate the general rule for the arithmetic sequence with
`a_(3)=-4` and
`a_(8)=-29`

A.]
`a_(n)=-6+(n-1)(-5)`
B.]
`a_(n)=-6+(n-1)(5)`
C.]
`a_(n)=6+(n-1)(-5)`
D.]
`a_(n)=6+(n-1)(5)`

Part 2.] Which of the following is the general term for the sequence m, -m, m, -m, . . .?
A.]
`m(-1)^(n-1)`
B.]
`(-m)^(n)`
C.]
`(-1)m^(n+1)`
D.]
`(-1)m^(n-1)`

Part 3.] Indicate a general rule for the
`n^(th)` term of the sequence when
`a_(1)=5` and
`r= √(3)`
A.]
`a_(n)=( √(3))(5)^(n+1)`
B.]
`a_(n)=( √(3))(5)^(n-1)`
C.]
`a_(n)=(5)( √(3))^(n-1)`
D.]
`a_(n)=(5)( √(3))^(n+1)`

Answer 1

These are 3 questions and 3 answers.

Part 1.] Indicate the general rule for the arithmetic sequence with A3 = - 4 and A8 = - 29

Answer: option C. An = 6 + (n-1)(-5)

Solution:

1) A3 is the third term
2) A8 is the eigth term
3) The formula for arithmetic sequences is: An = Ao + (n - 1)d

where n is the number of term and d is the difference between two consecutive terms.

=>

4) A8 = Ao + (8 - 1)d = - 29 => Ao + 7d = - 29 ----- [equation 1]

5) A3 = Ao + (3 - 1)d = - 4 => Ao + 2d = - 4 ------- [equation 2]

6) Subtract equation 2 from equation 1 => 7d - 2d = - 29 - (-4) =>

5d = - 29 + 4
5d = - 25
d = - 25/5 = - 5

7) Find Ao using equation 2:

Ao + 2d = - 4 =>
Ao = - 4 - 2d = - 4 - 2(- 5) = - 4 + 10 = 6

8) General rule: An = 6 + (n - 1) (-5) <-------- answer: option C.


Part 2.] Which of the following is the general term for the sequence m, -m, m, -m, . . .?

Answer: option a. m (-1)^ (n-1).

Justification:

the sign of the coefficient changes for each term.

when n = 1, the sign is positive: (-1)^ (1-1) = 1
when n = 2, the sign is negative: (-1)^ (2-1) = - 1
when n = 3, the sign is positive: (-1)^ (3-1) = 2

And so on. So, m (-1)^ (n-1) does the work.

Part 3.] Indicate a general rule for the nth term of the sequence when A1 = 5 and r = √3


Answer: option C. An = (5)(√3)^(n-1)

Step-by-step explanation:

This is a geometric sequence with A1 = 5 and r = √3

The terms of the geometric sequence are:

A1 = 5
A2 = A1 * √3 = 5√3
A3 = A2 * √3 = 5(√3)(√3) = 5(3) = 15
A4 = A3 * √3 = 15√3

So, the general expression is An = 5 * (√3)^(n-1), which is the option C.