MCQ
$x\sqrt {1 + y} + y\sqrt {1 + x} = 0$ માટે $\frac{{dy}}{{dx}} = ............$
  • A
    $\frac{1}{{{{\left( {1 + x} \right)}^2}}}$
  • $\frac{{ - 1}}{{{{\left( {1 + x} \right)}^2}}}$
  • C
    $\frac{1}{{1 + {x^2}}}$
  • D
    $\frac{{ - 1}}{{1 + {x^2}}}$

Answer

Correct option: B.
$\frac{{ - 1}}{{{{\left( {1 + x} \right)}^2}}}$
B

$x\sqrt{1+y}+y\sqrt{1+x}=0$

$\therefore x^2(1+y)=Y^2(1+x)$

$\therefore x^2+x^2y=y^2+y^2x$

$\therefore x^2-y^2=xy(y-x)$

$\therefore (x-y)(x+y)=-xy(x-y)$

$\therefore x+y=-xy \Rightarrow x+y+xy=0$

$\therefore x+y(1+x)=0 \Rightarrow y=\frac{-x}{1+x}$

$\therefore \frac{dy}{dx}=\frac{(1+x)(-1)+x}{(1+x^2)}=\frac{-1-x+x}{(1+x)^2}$

$=\frac{-1}{(1+x)^2}$

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