1/a-1 -1-a=[1-(a-1)(a+1)]/(a-1)=(2-a^2)/(a-1) (a/a^2-b^2-1/a+b)÷b/b-a=[a-(a-b)]/(a^2-b^2)*(b-a)/b=[b/(a-b)(a+b)][-(a-b)/b]=-1/(a+b)
