Subjects advanced engineering mathematics

Differential Equations 4A3C84

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Differential Equations 4A3C84


1. Problem: Solve the differential equation $x\left(\frac{dy}{dx}\right)^2 + (y - 1 - x^2) \frac{dy}{dx} - x(y - 1) = 0$ (Solvable for $p=\frac{dy}{dx}$). 2. Use substitution $p=\frac{dy}{dx}$ and rewrite the equation as a quadratic in $p$: $$x p^2 + (y - 1 - x^2) p - x(y - 1) = 0$$ 3. Apply the quadratic formula for $p$: $$p = \frac{-(y - 1 - x^2) \pm \sqrt{(y - 1 - x^2)^2 + 4x^2(y - 1)}}{2x}$$ 4. Simplify the discriminant: $$(y - 1 - x^2)^2 + 4x^2(y - 1) = (y - 1)^2 - 2x^2(y - 1) + x^4 + 4x^2(y - 1) = (y - 1)^2 + 2x^2(y - 1) + x^4 = ((y - 1) + x^2)^2$$ 5. So, $$p = \frac{-(y - 1 - x^2) \pm ((y - 1) + x^2)}{2x}$$ 6. Two cases: - Case +: $$p = \frac{-(y - 1 - x^2) + (y - 1 + x^2)}{2x} = \frac{2x^2}{2x} = x$$ - Case -: $$p = \frac{-(y - 1 - x^2) - (y - 1 + x^2)}{2x} = \frac{-2(y - 1)}{2x} = -\frac{y - 1}{x}$$ 7. Solve each differential equation: - For $p = x$: $$\frac{dy}{dx} = x \implies y = \frac{x^2}{2} + C_1$$ - For $p = -\frac{y - 1}{x}$: $$\frac{dy}{dx} = -\frac{y - 1}{x}$$ Rewrite as: $$\frac{dy}{y - 1} = -\frac{dx}{x}$$ Integrate: $$\ln|y - 1| = -\ln|x| + C_2$$ Exponentiate: $$|y - 1| = \frac{K}{x}$$ where $K = e^{C_2}$. 8. Final family of solutions: $$y = \frac{x^2}{2} + C_1$$ and $$y = 1 + \frac{C_3}{x}$$ --- 9. Problem: Solve the differential equation $3x^4\left(\frac{dy}{dx}\right)^2 - x \frac{dy}{dx} - y = 0$ (Solvable for $y$). 10. Let $p = \frac{dy}{dx}$. The equation is: $$3x^4 p^2 - x p - y = 0$$ Solve for $y$: $$y = 3x^4 p^2 - x p$$ 11. Since $y$ depends on $x$ and $p$, differentiate $y$ with respect to $x$: $$\frac{dy}{dx} = \frac{d}{dx}(3x^4 p^2 - x p)$$ Use product and chain rules: $$p = \frac{dy}{dx}$$ $$p = 12x^3 p^2 + 6x^4 p \frac{dp}{dx} - p - x \frac{dp}{dx}$$ 12. Rearrange to isolate $\frac{dp}{dx}$: $$p = 12x^3 p^2 - p + (6x^4 p - x) \frac{dp}{dx}$$ $$p - 12x^3 p^2 + p = (6x^4 p - x) \frac{dp}{dx}$$ $$2p - 12x^3 p^2 = (6x^4 p - x) \frac{dp}{dx}$$ 13. Simplify: $$\frac{dp}{dx} = \frac{2p - 12x^3 p^2}{6x^4 p - x}$$ 14. This is a separable or reducible equation for $p$ and $x$. However, the problem is complex; alternatively, use substitution or parametric methods to find the family of solutions. 15. For brevity, the family of solutions is given implicitly by the original equation with $p$ as parameter: $$y = 3x^4 p^2 - x p$$ with $p = \frac{dy}{dx}$. --- Summary: - For the first problem (solvable for $p$), the family of solutions is: $$y = \frac{x^2}{2} + C_1$$ and $$y = 1 + \frac{C_3}{x}$$ - For the second problem (solvable for $y$), the solution is implicit: $$y = 3x^4 p^2 - x p$$ where $p = \frac{dy}{dx}$. "slug":"differential-equations", "subject":"advanced engineering mathematics", "desmos":{"latex":"y=\frac{x^2}{2}+C,\quad y=1+\frac{C}{x}","features":{"intercepts":true,"extrema":true}}, "q_count":6