Explanation
We have,
$$ x+y=t-\dfrac{1}{t}\,\,......\,\,\left( 1 \right) $$
$$ {{x}^{2}}+{{y}^{2}}={{t}^{2}}+\dfrac{1}{{{t}^{2}}}\,\,.......\,\,\left( 2 \right) $$
By equation (2) to,
$$ {{x}^{2}}+{{y}^{2}}={{t}^{2}}+\dfrac{1}{{{t}^{2}}}-2+2 $$
$$ {{x}^{2}}+{{y}^{2}}={{\left( t-\dfrac{1}{t} \right)}^{2}}+2 $$
$$ {{x}^{2}}+{{y}^{2}}-2={{\left( t-\dfrac{1}{t} \right)}^{2}}\,\,.......\,\,\left( 3 \right) $$
By equation (1) and (3) to, and we get,
$$ {{x}^{2}}+{{y}^{2}}-2={{\left( x+y \right)}^{2}} $$
$$ {{x}^{2}}+{{y}^{2}}-2={{x}^{2}}+{{y}^{2}}+2xy $$
$$ -2=2xy $$
$$ xy=-1 $$
On differentiating and we get,
$$ x\dfrac{dy}{dx}+y\dfrac{dx}{dx}=0 $$
$$ x\dfrac{dy}{dx}+y\left( 1 \right)=0 $$
$$ x\dfrac{dy}{dx}=-y $$
$$ \dfrac{dy}{dx}=\dfrac{-y}{x} $$
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