解: AP=(x-1,y), AB=(-1,1), AP*AB=1-x+y BP=(x,y-1), BA=(1,-1), BP*BA=x+1-y 按题意:[1-(x-y)][1+(x-y)]=a 1-(x-y)^2=a (x-y)^2=1-a i) 当a>1 时,此题无解,即无满足条件的P点ii) 当a=1时, x-y=0 即P点坐标满足的关系式为 y=xiii)当0