If [math] \dfrac{x+1}{x-1}=\dfrac{a}{b} [/math] and [math]\dfrac{1-y}{1+y}=\dfrac{b}{a} [/math], then the value of [math] \dfrac{x-y}{1+xy}[/math] is?
If [math]y = (1 + x) ^ {\frac{1}{x}}[/math], then what will be the value of [math]\dfrac{dy}{dx}[/math]?