Find the general solution of: y'' - 4y' + 4y=e(2x)/x24y = e^(2x)/x² using variation of parameters.

Answer: y=c1e2x+c2xe2x−e2xln⁡∣x∣−e2xy = c_1e^{2x} + c_2xe^{2x} - e^{2x}\ln|x| - e^{2x}

Step-by-step solution

Step 1: Find the complementary solution

First, we find the complementary solution ycy_c by solving the homogeneous equation y′′−4y′+4y=0y'' - 4y' + 4y = 0. We form the characteristic equation m2−4m+4=0m^2 - 4m + 4 = 0, which factors as (m−2)2=0(m-2)^2 = 0. This gives us a repeated root m=2m=2. Therefore, the complementary solution is yc=c1e2x+c2xe2xy_c = c_1e^{2x} + c_2xe^{2x}.

Step 2: Identify y1y_1, y2y_2 and f(x)f(x)

From the complementary solution, we identify y1=e2xy_1 = e^{2x} and y2=xe2xy_2 = xe^{2x}. The non-homogeneous term f(x)f(x) is e2x/x2e^{2x}/x^2.

Step 3: Calculate the Wronskian

Next, we calculate the Wronskian W(y1,y2)W(y_1, y_2). The Wronskian is the determinant of the matrix formed by y1y_1, y2y_2 and their first derivatives. After computing the determinant, we find that the Wronskian is e4xe^{4x}.

Step 4: Calculate u1′u_1' and u2′u_2'

Using the formulas for variation of parameters, we calculate u1′u_1' and u2′u_2'. We substitute y1y_1, y2y_2, f(x)f(x), and WW into the formulas. After simplification, we get u1′=−1/xu_1' = -1/x and u2′=1/x2u_2' = 1/x^2.

Step 5: Integrate to find u1u_1 and u2u_2

Now, we integrate u1′u_1' and u2′u_2' to find u1u_1 and u2u_2. The integral of −1/x-1/x is −ln⁡∣x∣-\ln|x|, and the integral of 1/x21/x^2 is −1/x-1/x. We omit the constants of integration for the particular solution.

Step 6: Form the particular solution ypy_p

The particular solution ypy_p is given by u1y1+u2y2u_1 y_1 + u_2 y_2. Substituting the expressions for u1u_1, u2u_2, y1y_1, and y2y_2, we get yp=−e2xln⁡∣x∣−e2xy_p = -e^{2x}\ln|x| - e^{2x}.

Step 7: Write the general solution

Finally, the general solution is the sum of the complementary solution and the particular solution, y=yc+ypy = y_c + y_p. We combine the results to get the final general solution.

More from this chapter

All Differential Equations solutions →

Solve your own maths question free →