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QJEEM22Maa366: JEE Main 2022 Mathematics - Class 12 JEEM22Maa366 Solution: Let the solution curve of the differential equation , intersect …

Let the solution curve of the differential equation x \mathrm{~d} y=\left(\sqrt{x^{2}+y^{2}}+y\right) \mathrm{d} x, x>0 , intersect the line x=1x=1 at y=0y=0 and the line x=2x=2 at y=αy=\alpha . Then the value of α\alpha is :

Multiple Choice Options

  • A 12\frac{1}{2}
  • B 32\frac{3}{2}
  • C −- 32\frac{3}{2}
  • D 52\frac{5}{2}

Step-by-Step Verified Solution

xdy−ydxx2+y2=dx{{xdy - ydx} \over {\sqrt {{x^2} + {y^2}} }} = dx

⇒dydx=x2+y2x+yx\Rightarrow {{dy} \over {dx}} = {{\sqrt {{x^2} + {y^2}} } \over x} + {y \over x}

⇒dydx=1+y2x2+yx\Rightarrow {{dy} \over {dx}} = \sqrt {1 + {{{y^2}} \over {{x^2}}}} + {y \over x}

Let yx=v{y \over x} = v

⇒v+xdvdx=1+v2+v\Rightarrow v + x{{dv} \over {dx}} = \sqrt {1 + {v^2}} + v

⇒dv1+v2=dxx\Rightarrow {{dv} \over {\sqrt {1 + {v^2}} }} = {{dx} \over x}

OR ln⁡(v+1+v2)=ln⁡x+C\ln \left( {v + \sqrt {1 + {v^2}} } \right) = \ln x + C

at x=1, y=0x = 1,\,y = 0

⇒C=0\Rightarrow C = 0

yx+1+y2x2=x{y \over x} + \sqrt {1 + {{{y^2}} \over {{x^2}}}} = x

At x=2x = 2 ,

y2+1+y24=2{y \over 2} + \sqrt {1 + {{{y^2}} \over 4}} = 2

⇒1+y24=4+y24−2y\Rightarrow 1 + {{{y^2}} \over 4} = 4 + {{{y^2}} \over 4} - 2y

OR y=32y = {3 \over 2}

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