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3 years ago

Please help me out on this

Mathematics

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belka [17]3 years ago

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Consider the following. (A computer algebra system is recommended.) y'' + 3y' = 2t4 + t2e−3t + sin 3t (a) Determine a suitable f

drek231 [11]

First look for the fundamental solutions by solving the homogeneous version of the ODE:

$y''+3y'=0$

The characteristic equation is

$r^2+3r=r(r+3)=0$

with roots $r=0$ and $r=-3$ , giving the two solutions $C_1$ and $C_2e^{-3t}$ .

For the non-homogeneous version, you can exploit the superposition principle and consider one term from the right side at a time.

$y''+3y'=2t^4$

Assume the ansatz solution,

${y_p}=at^5+bt^4+ct^3+dt^2+et$

$\implies {y_p}'=5at^4+4bt^3+3ct^2+2dt+e$

$\implies {y_p}''=20at^3+12bt^2+6ct+2d$

(You could include a constant term f here, but it would get absorbed by the first solution $C_1$ anyway.)

Substitute these into the ODE:

$(20at^3+12bt^2+6ct+2d)+3(5at^4+4bt^3+3ct^2+2dt+e)=2t^4$

$15at^4+(20a+12b)t^3+(12b+9c)t^2+(6c+6d)t+(2d+e)=2t^4$

$\implies\begin{cases}15a=2\\20a+12b=0\\12b+9c=0\\6c+6d=0\\2d+e=0\end{cases}\implies a=\dfrac2{15},b=-\dfrac29,c=\dfrac8{27},d=-\dfrac8{27},e=\dfrac{16}{81}$

$y''+3y'=t^2e^{-3t}$

$e^{-3t}$ is already accounted for, so assume an ansatz of the form

$y_p=(at^3+bt^2+ct)e^{-3t}$

$\implies {y_p}'=(-3at^3+(3a-3b)t^2+(2b-3c)t+c)e^{-3t}$

$\implies {y_p}''=(9at^3+(9b-18a)t^2+(9c-12b+6a)t+2b-6c)e^{-3t}$

Substitute into the ODE:

$(9at^3+(9b-18a)t^2+(9c-12b+6a)t+2b-6c)e^{-3t}+3(-3at^3+(3a-3b)t^2+(2b-3c)t+c)e^{-3t}=t^2e^{-3t}$

$9at^3+(9b-18a)t^2+(9c-12b+6a)t+2b-6c-9at^3+(9a-9b)t^2+(6b-9c)t+3c=t^2$

$-9at^2+(6a-6b)t+2b-3c=t^2$

$\implies\begin{cases}-9a=1\\6a-6b=0\\2b-3c=0\end{cases}\implies a=-\dfrac19,b=-\dfrac19,c=-\dfrac2{27}$

$y''+3y'=\sin(3t)$

Assume an ansatz solution

$y_p=a\sin(3t)+b\cos(3t)$

$\implies {y_p}'=3a\cos(3t)-3b\sin(3t)$

$\implies {y_p}''=-9a\sin(3t)-9b\cos(3t)$

Substitute into the ODE:

$(-9a\sin(3t)-9b\cos(3t))+3(3a\cos(3t)-3b\sin(3t))=\sin(3t)$

$(-9a-9b)\sin(3t)+(9a-9b)\cos(3t)=\sin(3t)$

$\implies\begin{cases}-9a-9b=1\\9a-9b=0\end{cases}\implies a=-\dfrac1{18},b=-\dfrac1{18}$

So, the general solution of the original ODE is

$y(t)=\dfrac{54t^5 - 90t^4 + 120t^3 - 120t^2 + 80t}{405}\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,-\dfrac{3t^3+3t^2+2t}{27}e^{-3t}-\dfrac{\sin(3t)+\cos(3t)}{18}$

3 0

3 years ago

Thirty work orders are selected from a filing cabinet containing 500 work order folders by choosing every 15th folder. which sam

Andru [333]

It is Systematic sampling

5 0

3 years ago

A bottle of la belle bœuf contains 3/8 ounces of perfume. How many ounces of perfume would 4 1/2 bottles contain?

dusya [7]

ANSWER

$1 \frac{11}{16} ounces$

EXPLANATION

It was given that,a bottle of la belle bœuf contains 3/8 ounces of perfume.

We want to find how many ounces of perfume would 4 1/2 bottles contain.

If 1 bottle contains 3/8 ounces;

Then 4½ bottles should contain more ounces.

If more less divides.

4½ bottles contain

$\frac{4 \frac{1}{2} \times \frac{3}{8} }{1}$

$= \frac{27}{16}$

=1.6875 ounces.

3 0

3 years ago

Solve the system of equations. y = 9x y= 2x+56

nadya68 [22]

Answer:

(8, 72)

Step-by-step explanation:

Here we have two separate equations for y: y = 9x and y = 2x + 56.

Equating these equations eliminates y temporarily; we get:

9x = 2x + 56, or 7x = 56. Dividing both sides by 7 results in x = 8.

Then, by the first equation, y = 9(8) = 72.

The solution is (8, 72).

5 0

3 years ago

Solve for x 4x+8=6x−1 Give your answer as an improper fraction in its simplest form.

spin [16.1K]

Answer:

Step-by-step explanation:

4x+8=6x-1

-4x . =-4x .

8 = 2x-1

-1+8=2x-1+1

7=2x

7/2= 2x/2

3.5=x

4 0

3 years ago

Please help me out on this​

Please help me out on this