Differential Equation 66B034
1. **State the problem:** Solve the differential equation $$(6x - 3y + 2)dx + (2x - y - 1)dy = 0.$$
2. **Identify the type of equation:** This is a first-order differential equation in the form $$M(x,y)dx + N(x,y)dy = 0,$$ where $$M = 6x - 3y + 2$$ and $$N = 2x - y - 1.$$
3. **Check if the equation is exact:** Calculate $$\frac{\partial M}{\partial y}$$ and $$\frac{\partial N}{\partial x}.$$
- $$\frac{\partial M}{\partial y} = -3$$
- $$\frac{\partial N}{\partial x} = 2$$
Since $$\frac{\partial M}{\partial y} \neq \frac{\partial N}{\partial x},$$ the equation is not exact.
4. **Find an integrating factor:** Try an integrating factor depending on $$x$$ or $$y$$.
- Compute $$\frac{\partial N}{\partial x} - \frac{\partial M}{\partial y} = 2 - (-3) = 5.$$
- Compute $$\frac{M}{N} = \frac{6x - 3y + 2}{2x - y - 1}$$ which is not a function of $$x$$ or $$y$$ alone, so try $$\mu(y)$$ or $$\mu(x)$$.
- Check if $$\frac{\frac{\partial N}{\partial x} - \frac{\partial M}{\partial y}}{M} = \frac{5}{6x - 3y + 2}$$ is a function of $$x$$ alone (no), or if $$\frac{\frac{\partial M}{\partial y} - \frac{\partial N}{\partial x}}{N} = \frac{-5}{2x - y - 1}$$ is a function of $$y$$ alone (no).
5. **Try an integrating factor depending on $$x$$ and $$y$$:** Since simple methods fail, try to solve by rearranging or substitution.
6. **Rewrite the equation:**
$$ (6x - 3y + 2)dx + (2x - y - 1)dy = 0 $$
Divide both sides by $$dx$$ (assuming $$dx \neq 0$$):
$$ (6x - 3y + 2) + (2x - y - 1) \frac{dy}{dx} = 0 $$
So,
$$ \frac{dy}{dx} = - \frac{6x - 3y + 2}{2x - y - 1} $$
7. **Try substitution:** Let $$v = y/x$$, so $$y = vx$$ and $$\frac{dy}{dx} = v + x \frac{dv}{dx}.$$
Substitute into the equation:
$$ v + x \frac{dv}{dx} = - \frac{6x - 3(vx) + 2}{2x - v x - 1} = - \frac{6x - 3vx + 2}{2x - vx - 1} $$
Simplify numerator and denominator:
Numerator: $$6x - 3vx + 2 = x(6 - 3v) + 2$$
Denominator: $$2x - vx - 1 = x(2 - v) - 1$$
So,
$$ v + x \frac{dv}{dx} = - \frac{x(6 - 3v) + 2}{x(2 - v) - 1} $$
8. **Isolate $$x \frac{dv}{dx}$$:**
$$ x \frac{dv}{dx} = - \frac{x(6 - 3v) + 2}{x(2 - v) - 1} - v $$
9. **This is a complicated expression; however, the substitution reduces the problem to a separable or solvable form.** Further algebraic manipulation or numerical methods may be needed to solve explicitly.
**Final answer:** The differential equation can be transformed using substitution $$v = \frac{y}{x}$$ into
$$ x \frac{dv}{dx} = - \frac{x(6 - 3v) + 2}{x(2 - v) - 1} - v, $$
which can be further analyzed or solved by advanced methods.