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Chapter Differential Equation ​

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Answered by mathdude500
2

Given

 \tt \: \dfrac{dy}{dx}  = \dfrac{ {x}^{2}   +   {y}^{2} }{2xy}  -  -  - (i)

Since, degree of each term of numerator and denominator is same, therefore given differential equation is homogeneous.

 \tt \: Put \: y \:  =  \: vx   -  - (ii) \: \: \: in \: (i) \: we \: get

 \tt \: \dfrac{d}{dx}( vx) = \dfrac{ {x}^{2}   +   {(vx)}^{2} }{2x(vx)}

 \tt \: v\dfrac{d}{dx} x \:  +  \: x\dfrac{d}{dx} v \:  = \dfrac{ {x}^{2}   +   {v}^{2} {x}^{2}  }{2v {x}^{2} }

 \tt \: v + x \: \dfrac{dv}{dx}  = \dfrac{ {x}^{2} (1  +   {v}^{2}) }{2v {x}^{2} }

 \tt \: v + x \: \dfrac{dv}{dx}  = \dfrac{ (1  +   {v}^{2}) }{2v  }

 \tt \:  x \: \dfrac{dv}{dx}  = \dfrac{ (1  +   {v}^{2}) }{2v  }  - v

 \tt \:  x \: \dfrac{dv}{dx}  = \dfrac{ 1  +   {v}^{2}  -  {2v}^{2} }{2v  }

 \tt \:  x \: \dfrac{dv}{dx}  = \dfrac{ 1   -    {v}^{2}  }{2v  }

 \tt \: \dfrac{2v}{ {v}^{2} - 1 } dv =  - \dfrac{dx}{x}

On integrating both sides, we get

 \bf \:  \int\dfrac{2v}{ {v}^{2} - 1 } dv =  - \int \dfrac{dx}{x}

 \tt \:  log( {v}^{2}  - 1)  =  -  log(x)  +  log(c)

  \boxed{\red{\because \int \: \dfrac{f'(x)}{f(x)} dx =  log(f(x))  + c }}

 \boxed{\because{ \purple{ \int\dfrac{1}{x} dx =  log(x)  +  \: c}}}

 \tt \:  log |{v}^{2}  - 1|    +  log |x|    =  log(c)

 \tt \:  log  |({v}^{2}  - 1)x| =   log |c|

 \tt \: ({v}^{2}  - 1) x =   \pm \: c

On substituting the value of v, from equation (ii), we get

\bf\implies \:(\dfrac{ {y}^{2} }{ {x}^{2} }  - 1) \times x = \pm \:  c

\bf\implies \:(\dfrac{ {y}^{2}  -  {x}^{2} }{ {x}^{2} }  ) \times x =  \pm \: c

\bf\implies \:(\dfrac{ {y}^{2}  -  {x}^{2} }{ {x} }  ) = \pm \:  c

\bf\implies \: {y}^{2}  -  {x}^{2}  =  \pm \: cx

\bf\implies \: {y}^{2}  -  {x}^{2}  =   \: cx \:  \: or \: \bf\: {x}^{2}  -  {y}^{2}  =   \: cx

\large{\boxed{\boxed{\bf{Hence, Proved}}}}

Answered by julietiwari161
2

Answer:

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