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QJEEM06Ma422c: JEE Main 2006 Mathematics - Class 12 JEEM06Ma422c Solution: If then is

If xm.yn=(x+y)m+n,{x^m}.{y^n} = {\left( {x + y} \right)^{m + n}}, then dydx{{{dy} \over {dx}}} is

Multiple Choice Options

  • A yx{y \over x}
  • B x+yxy{{x + y} \over {xy}}
  • C xyxy
  • D xy{x \over y}

Step-by-Step Verified Solution

xm.yn=(x+y)m+n{x^m}.{y^n} = {\left( {x + y} \right)^{m + n}}

⇒mln⁡x+nln⁡y=(m+n)ln⁡(x+y)\Rightarrow m\ln x + n\ln y = \left( {m + n} \right)\ln \left( {x + y} \right)

Differentiating both sides.

∴\therefore mx+nydydx=m+nx+y(1+dydx){m \over x} + {n \over y}{{dy} \over {dx}} = {{m + n} \over {x + y}}\left( {1 + {{dy} \over {dx}}} \right)

⇒(mx−m+nx+y)=(m+nx+y−ny)dydx\Rightarrow \left( {{m \over x} - {{m + n} \over {x + y}}} \right) = \left( {{{m + n} \over {x + y}} - {n \over y}} \right){{dy} \over {dx}}

⇒my−nxx(x+y)=(my−nxy(x+y))dydx\Rightarrow {{my - nx} \over {x\left( {x + y} \right)}} = \left( {{{my - nx} \over {y\left( {x + y} \right)}}} \right){{dy} \over {dx}}

⇒dydx=yx\Rightarrow {{dy} \over {dx}} = {y \over x}

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