Math Problem Statement

Solve this Bernoulli lineal equation

Solve this Bernoulli linear equation

Solution

The equation shown in the image is:

dydx=3exy2\frac{dy}{dx} = -3 - e^x y^2

This is a Bernoulli differential equation, which has the form:

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

Here, the equation can be rearranged into a form that fits the Bernoulli equation structure. To solve it, we proceed as follows:

Step 1: Rewrite the equation

First, we can rewrite the given equation as:

dydx+exy2=3\frac{dy}{dx} + e^x y^2 = -3

Here, P(x)=0P(x) = 0 and Q(x)=exQ(x) = e^x, with n=2n = 2.

Step 2: Substitute v=y1n=y1v = y^{1-n} = y^{-1}

Let's define a new variable v=y1v = y^{-1}, so y=v1y = v^{-1} and dydx=v2dvdx\frac{dy}{dx} = -v^{-2} \frac{dv}{dx}.

Step 3: Substitution into the equation

Substitute into the original equation:

1v2dvdx+ex1v2=3-\frac{1}{v^2} \frac{dv}{dx} + e^x \frac{1}{v^2} = -3

Multiply through by v2-v^2 to simplify:

dvdx=3v2ex\frac{dv}{dx} = 3v^2 - e^x

Step 4: Solve the new linear equation

This equation is now linear in vv. The general approach to solve it is by using an integrating factor or a method appropriate for linear first-order differential equations.

However, let's move forward assuming you want an explicit integration process.

Step 5: Find the integrating factor

For an equation of the form:

dvdx+P(x)v=Q(x)\frac{dv}{dx} + P(x)v = Q(x)

we need to find the integrating factor μ(x)=eP(x)dx\mu(x) = e^{\int P(x) dx}. In this case, P(x)=3P(x) = -3.

So:

μ(x)=e3x\mu(x) = e^{-3x}

Step 6: Multiply the equation by the integrating factor

Multiply the equation by the integrating factor e3xe^{-3x}:

e3xdvdx3e3xv=e2xe^{-3x} \frac{dv}{dx} - 3e^{-3x} v = -e^{-2x}

This simplifies to:

ddx(ve3x)=e2x\frac{d}{dx}(v e^{-3x}) = -e^{-2x}

Step 7: Integrate both sides

Integrate both sides with respect to xx:

ve3x=e2xdxv e^{-3x} = \int -e^{-2x} dx

The integral on the right-hand side is:

e2xdx=12e2x+C\int -e^{-2x} dx = \frac{1}{2}e^{-2x} + C

So:

ve3x=12e2x+Cv e^{-3x} = \frac{1}{2}e^{-2x} + C

Step 8: Solve for vv

Solve for vv:

v=12ex+Ce3xv = \frac{1}{2}e^{x} + Ce^{3x}

Step 9: Substitute back v=y1v = y^{-1}

Finally, substitute v=y1v = y^{-1}:

y=112ex+Ce3xy = \frac{1}{\frac{1}{2}e^{x} + Ce^{3x}}

Thus, the solution to the differential equation is:

y(x)=2ex1+2Ce2xy(x) = \frac{2e^{-x}}{1 + 2Ce^{2x}}

Would you like more details or explanations on any of the steps?

Here are some related questions you might find interesting:

  1. What is the general form of a Bernoulli differential equation?
  2. How do you derive the integrating factor for a first-order linear differential equation?
  3. Can all Bernoulli equations be transformed into linear differential equations?
  4. What are the conditions for a differential equation to be exact?
  5. How do we solve a first-order separable differential equation?

Tip: Always verify your final solution by substituting it back into the original differential equation to ensure it satisfies the equation.

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Math Problem Analysis

Mathematical Concepts

Differential Equations
Bernoulli Equations
Linear Differential Equations

Formulas

Bernoulli equation: dy/dx + P(x)y = Q(x)y^n
Substitution: v = y^(1-n)
Integrating factor: μ(x) = e^∫P(x)dx

Theorems

Bernoulli Differential Equation Transformation
Integrating Factor Method

Suitable Grade Level

Undergraduate