...我想您是抄错题了呢.(x+y)(3y-y)这个.你再对对.我就知道!.[(x+2y)*-(x+y)(3x-y)-5y*]÷2x=[x*+4y*+4xy-(3x*+2xy-2y*)-5y*]÷2x=[x*+4y*+4xy-3x*-2xy+2y*-5y*]÷2x=[-2x*+2xy]÷2x=-x+y好了、就是这样的....