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CBSE Class 12 Math 2012 Solved Paper

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Question : 12 of 29
Marks: +1, -0
Solve the following differential equation:
2x2dxdy2x^2 \frac{dx}{dy} - 2xy + y2y^2 = 0
Solution:  
Here,
2x2dxdy2x^2 \frac{dx}{dy} - 2xy + y2y^2 = 0
dydx\frac{dy}{dx} = 2xyy22x2\frac{2xy - y^2}{2x^2}
Hence the given equation is an homogeneous equation.
Let y = vx
and dydx\frac{dy}{dx} = y + x dvdx\frac{dv}{dx}
So, v + x dvdx\frac{dv}{dx}
So, v + x dvdx\frac{dv}{dx} = 2x(vx)(vx)22x2\frac{2x(vx) - (vx)^2}{2x^2}
= 2vv22\frac{2v - v^2}{2} = vv22v - \frac{v^2}{2}
⇒ x dvdx\frac{dv}{dx} = - v22\frac{v^2}{2}
⇒ 2 ∫ 1v2\frac{1}{v^2} dv = ∫ dxx-\int \frac{dx}{x}
⇒ 2 (1v)\left(-\frac{1}{v}\right) = - log |x| + c
2xy\frac{2x}{y} = log |x| + c
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