(2x+a）/( x-1)- (x+2)/( x-2) =1
(2x+a）/( x-1)- (x+2)/( x-2) -1 = 0
{ (2x+a)(x-2) - (x+2)(x-1) -(x-1)( x-2) } / {(x-1)(x-2) = 0
{ (2x^2+ax-4x-2a) - (x^2+x-2) -(x^2-3x+2) } / {(x-1)(x-2) = 0
{ (a-2)x-2a) } / {(x-1)(x-2) = 0
x=2a/(a-2)
当a-2≠0,并且2a/(a-2)≠1,2a/(a-2)≠2时有解,解得：a≠2,且a≠-2
若改为无
则a-2=0,或2a/(a-2)=1,或2a/(a-2)=2
解得a=2,或a=-2