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This solution demonstrates how to solve a homogeneous differential equation using a substitution method.

Step-by-step solution

7 steps
  1. Identify the type of differential equation and apply the appropriate substitution.

    The given differential equation is dydx=x2+y2xy\frac{dy}{dx} = \frac{x^2+y^2}{xy}. This is a homogeneous differential equation because all terms in the numerator and denominator have the same degree (degree 2). For such equations, the standard substitution is y=vxy = vx.
    Differentiate y=vxy = vx with respect to xx using the product rule:

    dydx=v⋅dxdx+x⋅dvdx=v+xdvdx\frac{dy}{dx} = v \cdot \frac{dx}{dx} + x \cdot \frac{dv}{dx} = v + x \frac{dv}{dx}
  2. Substitute y=vxy=vx and dydx=v+xdvdx\frac{dy}{dx} = v + x \frac{dv}{dx} into the original differential equation.

    Substitute these expressions into dydx=x2+y2xy\frac{dy}{dx} = \frac{x^2+y^2}{xy}:

    v+xdvdx=x2+(vx)2x(vx)v + x \frac{dv}{dx} = \frac{x^2+(vx)^2}{x(vx)}
  3. Simplify the right-hand side of the equation.

    v+xdvdx=x2+v2x2vx2v + x \frac{dv}{dx} = \frac{x^2+v^2x^2}{vx^2}

    Factor out x2x^2 from the numerator:

    v+xdvdx=x2(1+v2)vx2v + x \frac{dv}{dx} = \frac{x^2(1+v^2)}{vx^2}

    Cancel out x2x^2:

    v+xdvdx=1+v2vv + x \frac{dv}{dx} = \frac{1+v^2}{v}
  4. Separate the variables vv and xx.

    Move vv from the left side to the right side:

    xdvdx=1+v2v−vx \frac{dv}{dx} = \frac{1+v^2}{v} - v

    Combine the terms on the right side by finding a common denominator:

    xdvdx=1+v2−v2vx \frac{dv}{dx} = \frac{1+v^2 - v^2}{v} xdvdx=1vx \frac{dv}{dx} = \frac{1}{v}

    Now, rearrange the equation so that all terms involving vv are on one side with dvdv, and all terms involving xx are on the other side with dxdx:

    v dv=1x dxv \, dv = \frac{1}{x} \, dx
  5. Integrate both sides of the separated equation.

    ∫v dv=∫1x dx\int v \, dv = \int \frac{1}{x} \, dx

    Perform the integration:

    v22=ln⁡∣x∣+C\frac{v^2}{2} = \ln|x| + C

    where CC is the constant of integration.

  6. Substitute back v=yxv = \frac{y}{x} to express the solution in terms of yy and xx.

    Replace vv with yx\frac{y}{x}:

    (yx)22=ln⁡∣x∣+C\frac{\left(\frac{y}{x}\right)^2}{2} = \ln|x| + C y22x2=ln⁡∣x∣+C\frac{y^2}{2x^2} = \ln|x| + C
  7. Rearrange the equation to solve for y2y^2.

    Multiply both sides by 2x22x^2:

    y2=2x2(ln⁡∣x∣+C)y^2 = 2x^2(\ln|x| + C)

    This is the general solution to the differential equation.

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