Q96 / 150 · MHT CET 2026 (15 April Shift 1) · Mathematics
The solution of the differential equation $x^2 \dfrac{dy}{dx} - xy = 1$ is...
- A$2xy - 2cx^2 - 1 = 0$
- B$2xy + 2cx^2 + 1 = 0$
- Correct answerC$2xy - 2cx^2 + 1 = 0$
- D$2x^2 y - 2cx + 1 = 0$
Solution
The given differential equation is $x^2 \dfrac{dy}{dx} - xy = 1$
Dividing by $x^2$, we get:
$\dfrac{dy}{dx} - \dfrac{1}{x}y = \dfrac{1}{x^2}$
This is a linear differential equation of the form $\dfrac{dy}{dx} + Py = Q$, where $P = -\dfrac{1}{x}$ and $Q = \dfrac{1}{x^2}$
Integrating Factor (IF) = $e^{\int P dx} = e^{\int -\dfrac{1}{x} dx} = e^{-\ln x} = \dfrac{1}{x}$
The solution is given by:
$y \cdot (\text{IF}) = \int Q \cdot (\text{IF}) dx + c$
$y \left(\dfrac{1}{x}\right) = \int \dfrac{1}{x^2} \left(\dfrac{1}{x}\right) dx + c$
$\dfrac{y}{x} = \int x^{-3} dx + c$
$\dfrac{y}{x} = \dfrac{x^{-2}}{-2} + c$
$\dfrac{y}{x} = -\dfrac{1}{2x^2} + c$
Multiplying the entire equation by $2x^2$, we get:
$2xy = -1 + 2cx^2$
$2xy - 2cx^2 + 1 = 0$
Answer: $2xy - 2cx^2 + 1 = 0$
Dividing by $x^2$, we get:
$\dfrac{dy}{dx} - \dfrac{1}{x}y = \dfrac{1}{x^2}$
This is a linear differential equation of the form $\dfrac{dy}{dx} + Py = Q$, where $P = -\dfrac{1}{x}$ and $Q = \dfrac{1}{x^2}$
Integrating Factor (IF) = $e^{\int P dx} = e^{\int -\dfrac{1}{x} dx} = e^{-\ln x} = \dfrac{1}{x}$
The solution is given by:
$y \cdot (\text{IF}) = \int Q \cdot (\text{IF}) dx + c$
$y \left(\dfrac{1}{x}\right) = \int \dfrac{1}{x^2} \left(\dfrac{1}{x}\right) dx + c$
$\dfrac{y}{x} = \int x^{-3} dx + c$
$\dfrac{y}{x} = \dfrac{x^{-2}}{-2} + c$
$\dfrac{y}{x} = -\dfrac{1}{2x^2} + c$
Multiplying the entire equation by $2x^2$, we get:
$2xy = -1 + 2cx^2$
$2xy - 2cx^2 + 1 = 0$
Answer: $2xy - 2cx^2 + 1 = 0$
Hence, the correct answer is option: 'C'.