연습 이미지

Amanita, let's break down the problem and solve it step by step.

Problem Understanding: We are given the differential equation:

x3y+x2y2xy+2y=2x4,x>0x^3 y''' + x^2 y'' - 2x y' + 2y = 2x^4, \quad x > 0

We are told that xx, x2x^2, and 1/x1/x are solutions to the homogeneous version (where the right side is 0). We are to find a particular solution to the nonhomogeneous equation.


Step-by-Step Solution Plan:

Step 1: Write the homogeneous equation.
Set the right side to zero:

x3y+x2y2xy+2y=0x^3 y''' + x^2 y'' - 2x y' + 2y = 0

Step 2: Find the general solution to the homogeneous equation.
Since xx, x2x^2, and 1/x1/x are solutions, the general solution to the homogeneous equation is:

yh=C1x+C2x2+C31xy_h = C_1 x + C_2 x^2 + C_3 \frac{1}{x}

where C1,C2,C3C_1, C_2, C_3 are constants.

Step 3: Find a particular solution to the nonhomogeneous equation.
The right side is 2x42x^4. We look for a particular solution, ypy_p, of the form Ax4A x^4 (since the right side is a polynomial and none of the homogeneous solutions are x4x^4).

Step 4: Substitute yp=Ax4y_p = A x^4 into the original equation and solve for AA.
We need to compute the derivatives:

  • yp=Ax4y_p = A x^4
  • yp=4Ax3y_p' = 4A x^3
  • yp=12Ax2y_p'' = 12A x^2
  • yp=24Axy_p''' = 24A x

Substitute these into the equation and solve for AA.


Let's execute these steps.

Step 4 Calculations:

Substitute into the equation:

x3(24Ax)+x2(12Ax2)2x(4Ax3)+2(Ax4)=2x4x^3 (24A x) + x^2 (12A x^2) - 2x (4A x^3) + 2(A x^4) = 2x^4

Let's simplify each term:

  • x3(24Ax)=24Ax4x^3 (24A x) = 24A x^4
  • x2(12Ax2)=12Ax4x^2 (12A x^2) = 12A x^4
  • 2x(4Ax3)=8Ax4-2x (4A x^3) = -8A x^4
  • 2(Ax4)=2Ax42(A x^4) = 2A x^4

Sum:

24Ax4+12Ax48Ax4+2Ax4=2x424A x^4 + 12A x^4 - 8A x^4 + 2A x^4 = 2x^4

(24A+12A8A+2A)x4=2x4(24A + 12A - 8A + 2A) x^4 = 2x^4

30Ax4=2x430A x^4 = 2x^4

Now, solve for AA:

30A=230A = 2

A=230=115A = \frac{2}{30} = \frac{1}{15}


Step 5: Write the particular solution.

So, the particular solution is:

yp=115x4y_p = \frac{1}{15} x^4

Final Answer:

Amanita, the particular solution to the given differential equation is:

yp=115x4\boxed{y_p = \frac{1}{15} x^4}