Help me plssssssssssssssssss

<img src="https://tex.z-dn.net/?f=%24a%2Ba%20r%2Ba%20r%5E%7B2%7D%2B%5Cldots%20%5Cinfty%3D15%24%24a%5E%7B2%7D%2B%28a%20r%29%5E%7B

riadik2000 [5.3K]

Let

$S_n = \displaystyle \sum_{k=0}^n r^k = 1 + r + r^2 + \cdots + r^n$

where we assume |r| < 1. Multiplying on both sides by r gives

$r S_n = \displaystyle \sum_{k=0}^n r^{k+1} = r + r^2 + r^3 + \cdots + r^{n+1}$

and subtracting this from $S_n$ gives

$(1 - r) S_n = 1 - r^{n+1} \implies S_n = \dfrac{1 - r^{n+1}}{1 - r}$

As n → ∞, the exponential term will converge to 0, and the partial sums $S_n$ will converge to

$\displaystyle \lim_{n\to\infty} S_n = \dfrac1{1-r}$

Now, we're given

$a + ar + ar^2 + \cdots = 15 \implies 1 + r + r^2 + \cdots = \dfrac{15}a$

$a^2 + a^2r^2 + a^2r^4 + \cdots = 150 \implies 1 + r^2 + r^4 + \cdots = \dfrac{150}{a^2}$

We must have |r| < 1 since both sums converge, so

$\dfrac{15}a = \dfrac1{1-r}$

$\dfrac{150}{a^2} = \dfrac1{1-r^2}$

Solving for r by substitution, we have

$\dfrac{15}a = \dfrac1{1-r} \implies a = 15(1-r)$

$\dfrac{150}{225(1-r)^2} = \dfrac1{1-r^2}$

Recalling the difference of squares identity, we have

$\dfrac2{3(1-r)^2} = \dfrac1{(1-r)(1+r)}$

We've already confirmed r ≠ 1, so we can simplify this to

$\dfrac2{3(1-r)} = \dfrac1{1+r} \implies \dfrac{1-r}{1+r} = \dfrac23 \implies r = \dfrac15$

It follows that

$\dfrac a{1-r} = \dfrac a{1-\frac15} = 15 \implies a = 12$

and so the sum we want is

$ar^3 + ar^4 + ar^6 + \cdots = 15 - a - ar - ar^2 = \boxed{\dfrac3{25}}$

which doesn't appear to be either of the given answer choices. Are you sure there isn't a typo somewhere?

7 0

2 years ago

Prove if the sum of the digits of a 3 digit number n is divisible by 9, then n is divisible by 9.

beks73 [17]

$n=100x+10y+z\\x+y+z=9k,k\in\mathbb{Z}\\\\n=99x+9y+x+y+z\\n=99x+9y+9k\\n=9(11x+y+k)$

6 0

3 years ago

The following condensed information was reported by Peabody Toys, Inc., for 2021 and 2020: ($ in thousands) 2021 2020 Income sta

never [62]

Answer:

The answers are given below.

Step-by-step explanation:

The computation is shown below:

1.a.

Profit Margin = Net Income ÷ Sales × 100

= $374 ÷ $6,900 ×100

= 5.4%

1-b:

Average Assets = (Beginning Assets + Ending Assets) ÷ 2

= ($3,200 + $3,600) ÷ 2

= $3,400

Now

Return on Assets = Net Income ÷ Average Assets

= $374 ÷ $3,400

= 11%

1-c

Average Equity = ($700 + $700 + $320 + $270) ÷ 2

= $995

Now

Return on Equity = Net Income ÷ Average Equity *100

= $374 ÷ $995

= 37.59%

2:

Dividends Paid = Beginning Retained Earnings + Net Income – Ending Retained Earnings

= $270 + $374 - $320

= $324

4 0

3 years ago

A student needs to earn 80 points on the test in order to keep an A grade for the semester. Write an equation that represents th

Annette [7]

The most simple way is to get 8 questions right on a ten question test. 8q/10q = 80%.

4 0

3 years ago

PLS HELP ANSWER THIS QUESTION ITS ALGEBRA 1

Vladimir79 [104]

Answer:

The minus 3 in the square will shift the graph to the right 3 x-coordinates and the minus 8 in the outside will move the graph downwards by 8 y-coordinates.

Step-by-step explanation:

The minus 3 in the square will shift the graph to the right 3 x-coordinates and the minus 8 in the outside will move the graph downwards by 8 y-coordinates.

4 0

3 years ago