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3 years ago

6

Christiana and Marlena opened their first savings accounts on the same day. Christiana opened her account with $55 and plans to

deposit $10 every month. Marlena opened her account with $20 and plans to deposit $15 every month. After how many months will their two accounts have the same amount of money? What will that amount be?
The two accounts will have the same amount of money in BLANK months. And, the amount will be $ BLANK

2 answers:

PolarNik [594]3 years ago

8 0

Answer: it will take 4 months for the amount to be the same and the amount would be $95

Step-by-step explanation:

Let x represent the number if months it will take for the two accounts have the same amount of money.

Christiana opened her account with $55 and plans to deposit $10 every month. This means that the amount that in the account after x months would be

10x + 55

Marlena opened her account with $35 and plans to deposit $15 every month. This means that the amount that in the account after x months would be

15x + 35

For the amount in the accounts to be the same, the number of months would be

15x + 35 = 10x + 55

15x - 10x = 55 - 35

5x = 20

x = 20/5

x = 4

The amount would be

15 × 4 + 35

= 60 + 35

= $95

Ivenika [448]3 years ago

8 0

It will take 4 months for the amount to be the same and the amount would be $95

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3 years ago

A. Find the amplitude.

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Answers:

a) Amplitude = 2
b) Period = pi
c) Vertical shift = -2, which means it has been shifted down 2 units.
d) Horizontal shift = 3pi/8, this shifting is to the right.
e) There is <u> one </u> cycle between 0 and 2pi.
f) The equation of the graph is y = 2*sin(2(x-3pi/8))-2

========================================================

Explanations:

Part (a)

The highest point is when y = 0 and the lowest point is when y = -4. The vertical distance between the peak and valley is 4 units, which cuts in half to 2. This is the amplitude. It's the vertical distance from the center to either the peak or valley.

Note: Amplitude is always positive as it measures a distance.

---------------------

Part (b)

For x > 0, the first valley or lowest point occurs between 0 and pi/4. It appears to be the midpoint of the two values. So that would be (0+pi/4)/2 = pi/8.

The next valley occurs between pi and 5pi/4. Compute the midpoint to get (pi+5pi/4)/2 = (4pi/4+5pi/4)/2 = (9pi/4)/2 = 9pi/8

So we have the graph go from one valley x = pi/8 to the next valley over x = 9pi/8. This is a distance of pi units because 9pi/8-pi/8 = 8pi/8 = pi

The graph repeats itself every pi units, so the period is pi.

---------------------

Part (c)

The midline is normally through y = 0, aka the x axis. However, the graph shows the midline is through y = -2. This means the graph has been shifted down 2 units.

---------------------

Part (d)

This will depend on whether you use sine or cosine. This is entirely because cosine is a phase-shifted version of sine, and vice versa. I'll go with sine.

The parent sine function y = sin(x) goes through the origin (0,0)

However, as part (c) mentioned, we shifted the graph 2 units down. So we have y = sin(x)-2. But plugging x = 0 into this leads to the point (0,-2)

This doesn't match what the graph says. The graph shows the point (3pi/8, -2) on the red curve. The x coordinate 3pi/8 is the midpoint of pi/4 and pi/2

This must mean we need to shift the sine graph 3pi/8 units to the right.

---------------------

Part (e)

Start at the lowest point when x = pi/8. If you start the cycle here, then it ends when x = 9pi/8. See part (b).

So far we've completed one cycle. If we start at x = 9pi/8, then the next valley or lowest point is slightly beyond or to the right of x = 2pi. This means we run out of room and we haven't completed a full cycle.

Overall, one full cycle is between 0 and 2pi.

---------------------

Part (f)

Again I'm going to use sine instead of cosine. Refer back to part (d).

The general sine curve equation is

y = A*sin(B(x-C))+D

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|A| = amplitude
B handles the period, specifically T = 2pi/B where T is the period. We can solve for B to get B = 2pi/T
C = horizontal phase shift
D = vertical shift, and ties together with the midline equation

In this case, we found that

|A| = 2
T = pi leads to B = 2pi/T = 2pi/pi = 2
C = 3pi/8
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So,

y = A*sin(B(x-C))+D

will update to

y = 2*sin(2(x-3pi/8))-2

which is one way to express the equation of the red curve. Optionally you can distribute the 2 through to (x-3pi/8).

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