(x平方—2x分之x+2-x平方-4x+4分之x—1)除以x分之x-4
=[(x+2)/x(x-2) -(x-1)/(x-2)^2]除以x分之x-4
=[((x+2)(x-2)-x(x-1))/x(x-2)^2]* x/(x-4)
=[(x^2-4-x^2+x)/x(x-2)^2]* x/(x-4)
=[(x-4)/x(x-2)^2]* x/(x-4)
=1/(x-2)^2