Math Problem Statement

dy/dx = y^3 / x+1

Solution

The given differential equation is:

dydx=y3x+1.\frac{dy}{dx} = \frac{y^3}{x+1}.

This is a separable differential equation, which we can solve by separating the variables yy and xx. Let's solve it step by step.


Step 1: Rearrange to separate variables

Rewriting the equation: 1y3dy=1x+1dx.\frac{1}{y^3} \, dy = \frac{1}{x+1} \, dx.


Step 2: Integrate both sides

We integrate each side: 1y3dy=1x+1dx.\int \frac{1}{y^3} \, dy = \int \frac{1}{x+1} \, dx.

Left-hand side:

1y3dy=y3dy=y22=12y2.\int \frac{1}{y^3} \, dy = \int y^{-3} \, dy = \frac{y^{-2}}{-2} = -\frac{1}{2y^2}.

Right-hand side:

1x+1dx=lnx+1.\int \frac{1}{x+1} \, dx = \ln|x+1|.


Step 3: Combine results

After integrating, we have: 12y2=lnx+1+C,-\frac{1}{2y^2} = \ln|x+1| + C, where CC is the constant of integration.


Step 4: Solve for y2y^2 (optional)

Multiply through by 2-2 to simplify: 1y2=2lnx+12C.\frac{1}{y^2} = -2\ln|x+1| - 2C.

Let C1=2CC_1 = -2C (absorbing constants): 1y2=2lnx+1+C1.\frac{1}{y^2} = -2\ln|x+1| + C_1.

Invert to find y2y^2: y2=12lnx+1+C1.y^2 = \frac{1}{-2\ln|x+1| + C_1}.

Finally, take the square root: y=±12lnx+1+C1.y = \pm \sqrt{\frac{1}{-2\ln|x+1| + C_1}}.


This is the general solution. Let me know if you'd like further details or clarification!


Related Questions:

  1. How do we interpret constants of integration in solutions?
  2. Can this equation be solved for specific initial conditions?
  3. What happens if x=1x = -1? Does the solution still hold?
  4. How do we solve non-separable differential equations?
  5. Can we visualize this solution graphically?

Tip:

When solving separable equations, always check if the variables are separable before attempting other methods!

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Math Problem Analysis

Mathematical Concepts

Differential Equations
Separable Equations
Integration

Formulas

Separation of Variables: (1/y^n) dy = (1/x^m) dx
Integral of y^n: ∫ y^n dy = y^(n+1)/(n+1)
Integral of 1/x: ∫ (1/x) dx = ln|x|

Theorems

Fundamental Theorem of Calculus
Separation of Variables Method

Suitable Grade Level

Grades 11-12 (Advanced High School) or Early College