Use variation of parameters to find the general solution of the differential equation x2 y′′− x y′ =x3 ex if two solutions to the associated homogeneous problem are known to be 1 and x2
Question
Use variation of parameters to find the general solution of the differential equation x2 y′′− x y′ =x3 ex if two solutions to the associated homogeneous problem are known to be 1 and x2
Solution
Sure, let's solve the given differential equation using the method of variation of parameters.
The given differential equation is x²y'' - xy' = x³eˣ.
The associated homogeneous differential equation is x²y'' - xy' = 0.
We are given that the solutions to the homogeneous differential equation are y₁ = 1 and y₂ = x².
Step 1: Write down the Wronskian of y₁ and y₂.
W = det[y₁ y₂; y₁' y₂'] = det[1 x²; 0 2x] = 2x.
Step 2: Find u₁ and u₂ using the formulas:
u₁' = -y₂f/W = -x²(x³eˣ)/(2x) = -x²eˣ/2,
u₂' = y₁f/W = (x³eˣ)/(2x) = x²eˣ/2.
Step 3: Integrate u₁' and u₂' to find u₁ and u₂:
u₁ = ∫u₁'dx = ∫-x²eˣ/2 dx = -1/2 ∫x²eˣ dx,
u₂ = ∫u₂'dx = ∫x²eˣ/2 dx = 1/2 ∫x²eˣ dx.
Step 4: Use the formula for the solution of the non-homogeneous differential equation:
y = y₁u₁ + y₂u₂ = u₁ + x²u₂.
This is the general solution of the given differential equation.
Note: The integrals ∫x²eˣ dx in the expressions for u₁ and u₂ can be computed using the method of integration by parts.
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