x+2/x@-2x - x+1/x@-4x+4
=X+2/X(X-2)-X+1/(X-2)@
=(X+2)(X-2)/X(X-2)@-X(X+1)/X(X-2)@
=X@-4-X@-X/X(X-2)@
=-(x+4)/X(X-2)@
@为平方