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)= .