Answer: Infinite solutions
Step-by-step explanation:
Answers:
- a) 15000 represents the starting amount
- b) The decay rate is 16%, which means the car loses 16% of its value each year.
- c) x is the number of years
- d) f(x) is the value of the car after x years have gone by
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Explanation:
We have the function f(x) = 15000(0.84)^x. If we plug in x = 0, then we get,
f(x) = 15000(0.84)^x
f(0) = 15000(0.84)^0
f(0) = 15000(1)
f(0) = 15000
In the third step, I used the idea that any nonzero value to the power of 0 is always 1. The rule is x^0 = 1 for any nonzero x.
So that's how we get the initial value of the car. The car started off at $15,000.
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The growth or decay rate depends entirely on the base of the exponential, which is 0.84; compare it to 1+r and we see that 1+r = 0.84 solves to r = -0.16 which converts to -16%. The negative indicates the value is going down each year. So we have 16% decay or the value is going down 16% per year.
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The value of x is the number of years. In the first section, x = 0 represented year 0 or the starting year. If x = 1, then one full year has passed by. For x = 2, we have two full years pass by, and so on.
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The value of f(x) is the value of the car after x years have gone by. We found that f(x) = 15000 when x = 0. In other words, at the start the car is worth $15,000. Plugging in other x values leads to other f(x) values. For example, if x = 2, then you should find that f(x) = 10584. This means the car is worth $10,584 after two years.
Answer:
So, solution of the differential equation is
![y(t)=-\frac{5x^2}{4}\cot 2x\cdot \cos 2x+c_1e^{-2it}+c_2e^{2it}\\](https://tex.z-dn.net/?f=y%28t%29%3D-%5Cfrac%7B5x%5E2%7D%7B4%7D%5Ccot%202x%5Ccdot%20%5Ccos%20%202x%2Bc_1e%5E%7B-2it%7D%2Bc_2e%5E%7B2it%7D%5C%5C)
Step-by-step explanation:
We have the given differential equation: y′′+4y=5xcos(2x)
We use the Method of Undetermined Coefficients.
We first solve the homogeneous differential equation y′′+4y=0.
![y''+4y=0\\\\r^2+4=0\\\\r=\pm2i\\\\](https://tex.z-dn.net/?f=y%27%27%2B4y%3D0%5C%5C%5C%5Cr%5E2%2B4%3D0%5C%5C%5C%5Cr%3D%5Cpm2i%5C%5C%5C%5C)
It is a homogeneous solution:
![y_h(t)=c_1e^{-2i t}+c_2e^{2i t}](https://tex.z-dn.net/?f=y_h%28t%29%3Dc_1e%5E%7B-2i%20t%7D%2Bc_2e%5E%7B2i%20t%7D)
Now, we finding a particular solution.
![y_p(t)=A5x\cos 2x\\\\y'_p(t)=A5\cos 2x-A10x\sin 2x\\\\y''_p(t)=-A20\sin 2x-A20x\cos 2x\\\\\\\implies y''+4y=5x\cos 2x\\\\-A20\sin 2x-A20x\cos 2x+4\cdot A5x\cos 2x=5x\cos 2x\\\\-A20\sin 2x=5x\cos 2x\\\\A=-\frac{x}{4} \cot 2x\\](https://tex.z-dn.net/?f=y_p%28t%29%3DA5x%5Ccos%202x%5C%5C%5C%5Cy%27_p%28t%29%3DA5%5Ccos%202x-A10x%5Csin%202x%5C%5C%5C%5Cy%27%27_p%28t%29%3D-A20%5Csin%202x-A20x%5Ccos%202x%5C%5C%5C%5C%5C%5C%5Cimplies%20y%27%27%2B4y%3D5x%5Ccos%202x%5C%5C%5C%5C-A20%5Csin%202x-A20x%5Ccos%202x%2B4%5Ccdot%20A5x%5Ccos%202x%3D5x%5Ccos%202x%5C%5C%5C%5C-A20%5Csin%202x%3D5x%5Ccos%202x%5C%5C%5C%5CA%3D-%5Cfrac%7Bx%7D%7B4%7D%20%5Ccot%202x%5C%5C)
we get
![y_p(t)=A5\cos 2x\\\\y_p(t)=-\frac{5x^2}{4}\cot 2x\cdot \cos 2x\\\\\\y(t)=y_p(t)+y_h(t)\\\\y(t)=-\frac{5x^2}{4}\cot 2x\cdot \cos 2x+c_1e^{-2it}+c_2e^{2it}\\](https://tex.z-dn.net/?f=y_p%28t%29%3DA5%5Ccos%202x%5C%5C%5C%5Cy_p%28t%29%3D-%5Cfrac%7B5x%5E2%7D%7B4%7D%5Ccot%202x%5Ccdot%20%5Ccos%20%202x%5C%5C%5C%5C%5C%5Cy%28t%29%3Dy_p%28t%29%2By_h%28t%29%5C%5C%5C%5Cy%28t%29%3D-%5Cfrac%7B5x%5E2%7D%7B4%7D%5Ccot%202x%5Ccdot%20%5Ccos%20%202x%2Bc_1e%5E%7B-2it%7D%2Bc_2e%5E%7B2it%7D%5C%5C)
So, solution of the differential equation is
![y(t)=-\frac{5x^2}{4}\cot 2x\cdot \cos 2x+c_1e^{-2it}+c_2e^{2it}\\](https://tex.z-dn.net/?f=y%28t%29%3D-%5Cfrac%7B5x%5E2%7D%7B4%7D%5Ccot%202x%5Ccdot%20%5Ccos%20%202x%2Bc_1e%5E%7B-2it%7D%2Bc_2e%5E%7B2it%7D%5C%5C)
How to solve your problem
9−4+3
9x−4+3x9x-4+3x9x−4+3x
Simplify
1
Combine like terms
9−4+3
9x−4+3x{\color{#c92786}{9x}}-4+{\color{#c92786}{3x}}9x−4+3x
12−4
12x−4{\color{#c92786}{12x}}-412x−4
Solution
12−4
SO D