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Bernoulli Differential Equations

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Standard form of a Bernoulli equation

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The standard form is y′+P(x)y=Q(x)yny'+P(x)y=Q(x)y^n. To solve, use the substitution v=y1−nv = y^{1-n} which turns it into a linear differential equation.

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Basic Bernoulli equation y′+y=y2y' + y = y^2

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Use the substitution v=y−1v = y^{-1}. The equation becomes v′−v=−1v' - v = -1, which has a solution v=Ce−x−1v = Ce^{-x} - 1. Hence, y=1Ce−x−1y = \frac{1}{Ce^{-x} - 1}.

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Bernoulli equation with exponential functions y′−2y=−e2xy3y' - 2y = -e^{2x}y^3

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Substitute v=y−2v = y^{-2}. The transformed equation is v′+4v=2e2xv' + 4v = 2e^{2x}, which can be solved using an integrating factor to find vv. Then reverse the substitution for yy.

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Solve y′+4xy=2x2y2y' + \frac{4}{x}y = \frac{2}{x^2}y^2

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Apply the substitution v=y−1v = y^{-1}. The new equation v′−4xv=−2x2v' - \frac{4}{x}v = - \frac{2}{x^2} can be solved. The final solution for yy involves combining constants and applying the initial conditions.

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Handling an equation of the form xy′−y=x3y3xy' - y = x^3y^3

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Use the substitution v=y−2v = y^{-2} to linearize the equation to xv′+2v=x3xv' + 2v = x^3. Solve for vv using integrating factor or other means, then find yy from vv.

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Bernoulli equation example with trigonometric functions y′+tan⁡(x)y=sin⁡(x)y4y' + \tan(x)y = \sin(x)y^4

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The substitution v=y−3v = y^{-3} linearizes the equation to v′−3tan⁡(x)v=−3sin⁡(x)v' - 3\tan(x)v = -3\sin(x). After finding vv, the solution for yy is found by reversing the substitution.

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Transforming dydx+yx=xy2\frac{dy}{dx} + \frac{y}{x} = xy^2 to solve for yy

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Substitute v=y−1v = y^{-1} which converts the equation to v′−vx=−xv' - \frac{v}{x} = -x. Solve the linear ODE for vv and then reverse the substitution to find yy.

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Solving y′+3y=6x2y5y' + 3y = 6x^2y^5

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Take v=y−4v = y^{-4} as the substitution, which turns the equation into v′−12v=−6x2v' - 12v = -6x^2. Solve for vv using an integrating factor, then find yy by transforming back from vv.

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Working with a negative exponent y′−y=−y−2y' - y = -y^{-2}

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Substitute v=y3v = y^3 to get a linear equation v′−3v=−3v' - 3v = -3. Solve for vv, and then calculate yy given that v=y3v = y^3.

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General solution approach for dydx+P(x)y=Q(x)yn\frac{dy}{dx} + P(x)y = Q(x)y^n

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The substitution v=y1−nv = y^{1-n} transforms the Bernoulli equation into a linear equation v′+(1−n)P(x)v=(1−n)Q(x)v'+(1-n)P(x)v=(1-n)Q(x). After finding v(x)v(x), solve for yy using the relationship between vv and yy.

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