通分 a(x-y)分之x,b(y-x)分之y

问题描述:

通分 a(x-y)分之x,b(y-x)分之y

公因式为ab(x-y)
即bx/[ab(x-y)]
y/ b(y-x)=-y/b(x-y)=-ay/[ab(x-y)]