2) ((a-(1+a²)/(a-1)) *(a-1)/(a+1)² =( (a² -a -1-a²)/(a-1) ) *(a-1)/(a+1)² =
(-(a+1)/(a-1)) * (a-1)/(a+1)² = -1/(a+1).
3) ( 1/(b² -b) -1/(b-1)) *b/(b+2) +b/(b² -4) = ( 1/(b(b -1) -1/(b-1)) *b/(b+2) +b/(b² -4) =
(( 1-b)/b(b-1))* b/(b+2) +b/(b² -4)² = -1/(b+2) +b/(b² -4) =(2-b+b)/(b²-4) =2/(b² -4).