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The general solution of the differential equation ydx−(x+2y2)dy=0ydx - (x + 2y^2)dy = 0

Solution

✅ Correct Option: 4

Given differential equation: ydx−(x+2y2)dy=0ydx - (x + 2y^2)dy = 0


ydx=(x+2y2)dyydx = (x + 2y^2)dy

dxdy=x+2y2y\frac{dx}{dy} = \frac{x + 2y^2}{y}

dxdy=xy+2y\frac{dx}{dy} = \frac{x}{y} + 2y


dxdy−xy=2y\frac{dx}{dy} - \frac{x}{y} = 2y

This is in the standard linear form dxdy+P(y)⋅x=Q(y)\frac{dx}{dy} + P(y) \cdot x = Q(y) where P(y)=−1yP(y) = -\frac{1}{y} and Q(y)=2yQ(y) = 2y


The integrating factor is:

IF=e∫P(y)dyIF = e^{\int P(y)dy}

IF=e∫−1ydyIF = e^{\int -\frac{1}{y}dy}

IF=e−ln⁡yIF = e^{-\ln y}

IF=eln⁡y−1IF = e^{\ln y^{-1}}

IF=1yIF = \frac{1}{y}


1y⋅dxdy−1y⋅xy=1y⋅2y\frac{1}{y} \cdot \frac{dx}{dy} - \frac{1}{y} \cdot \frac{x}{y} = \frac{1}{y} \cdot 2y

1ydxdy−xy2=2\frac{1}{y}\frac{dx}{dy} - \frac{x}{y^2} = 2

The left side is the derivative of xy\frac{x}{y}:

ddy(xy)=2\frac{d}{dy}\left(\frac{x}{y}\right) = 2


∫ddy(xy)dy=∫2 dy\int \frac{d}{dy}\left(\frac{x}{y}\right)dy = \int 2 \, dy

xy=2y+C\frac{x}{y} = 2y + C

x=2y2+Cyx = 2y^2 + Cy


Therefore, the general solution is x=2y2+Cyx = 2y^2 + Cy where CC is the constant of integration.

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