Does anyone know the answer to this please help A,B,C, or D???!!?

Determine formula of the nth term 2, 6, 12 20 30,42

nalin [4]

Check the forward differences of the sequence.

If $\{a_n\} = \{2,6,12,20,30,42,\ldots\}$ , then let $\{b_n\}$ be the sequence of first-order differences of $\{a_n\}$ . That is, for n ≥ 1,

$b_n = a_{n+1} - a_n$

so that $\{b_n\} = \{4, 6, 8, 10, 12, \ldots\}$ .

Let $\{c_n\}$ be the sequence of differences of $\{b_n\}$ ,

$c_n = b_{n+1} - b_n$

and we see that this is a constant sequence, $\{c_n\} = \{2, 2, 2, 2, \ldots\}$ . In other words, $\{b_n\}$ is an arithmetic sequence with common difference between terms of 2. That is,

$2 = b_{n+1} - b_n \implies b_{n+1} = b_n + 2$

and we can solve for $b_n$ in terms of $b_1=4$ :

$b_{n+1} = b_n + 2$

$b_{n+1} = (b_{n-1}+2) + 2 = b_{n-1} + 2\times2$

$b_{n+1} = (b_{n-2}+2) + 2\times2 = b_{n-2} + 3\times2$

and so on down to

$b_{n+1} = b_1 + 2n \implies b_{n+1} = 2n + 4 \implies b_n = 2(n-1)+4 = 2(n + 1)$

We solve for $a_n$ in the same way.

$2(n+1) = a_{n+1} - a_n \implies a_{n+1} = a_n + 2(n + 1)$

Then

$a_{n+1} = (a_{n-1} + 2n) + 2(n+1) \\ ~~~~~~~= a_{n-1} + 2 ((n+1) + n)$

$a_{n+1} = (a_{n-2} + 2(n-1)) + 2((n+1)+n) \\ ~~~~~~~ = a_{n-2} + 2 ((n+1) + n + (n-1))$

$a_{n+1} = (a_{n-3} + 2(n-2)) + 2((n+1)+n+(n-1)) \\ ~~~~~~~= a_{n-3} + 2 ((n+1) + n + (n-1) + (n-2))$

and so on down to

$a_{n+1} = a_1 + 2 \displaystyle \sum_{k=2}^{n+1} k = 2 + 2 \times \frac{n(n+3)}2$

$\implies a_{n+1} = n^2 + 3n + 2 \implies \boxed{a_n = n^2 + n}$

6 0

2 years ago

5 = 5(y - 2)<br>A. -3<br>B. 3<br>C. -1<br>D. 1

Bess [88]

Answer:

Its 3

Step-by-step explanation:

8 0

3 years ago

Read 2 more answers

Find the value of each trigonometric ratio. 18) cos X Y 24 24 25 24 A) C) 25 B) D) 24 25 25

irina [24]

Answer:

Step-by-step explanation:

3 0

2 years ago

Please answer all part correct

insens350 [35]

Answer:

a). We want to know how much each point was worth.

b). $12x+5=41$

c). Each problem worth 3 points.

Step-by-step explanation:

a). We want to know how much each problem was worth. Because we have the total points of the test, and how much was the bonus. But we still don't know the worth of each problem.

b). We know that the total points of the test were 41, and the bonus 5 points. There were 12 problems on the test and we are going to use "x" for the unknown part (how many points each problem was worth).

The equation is :

$12x+5=41$

Why 12x? Because if you multiply the twelve problems of the test with the worth of each one and then add the 5 points of the bonus you will obtain the total points of the test (41).

c). Now we have to solve the equation, this means that we have to clear "x":

$12x+5=41$

Subtract 5 from both sides.

$12x+5-5=41-5\\12x=36$