交点b应该是（0,-4）吧,否则0a不可能等于ab将b(0,-4)带入y=kx+b得：b=-4将y=mx带入y=kx-4得：mx=kx-4x=4/(k-m)则a（4/(k-m),4m/(k-m))又oa=ab所以 16/(k-m)^2+16m^2/(k-m)^2=16(k-m)^2+[4m/(k-m)+4]^2 (两点的距离公...