Упрости

а) \((x-1)\left(\dfrac{1}{x}+1\right)=\) [ ];

б) \(\left(\dfrac{a}{b}-1\right)(a+b)=\) [ ];

в) \(\left(y+\dfrac{1}{y}\right)\left(y-\dfrac{1}{y}\right)=\) [ ];

г) \(\left(x-\dfrac{1}{y}\right)\left(x+\dfrac{1}{y}\right)=\) [ ].