X^2+2(M+1)X+3M^2+4MN+4N^2+2=(X+M+1)^2-M^2-2M-1+3M^2+4MN+4N^2+2=(X+M+1)^2+M^2-2M+1 +M^2+4MN+4N^2=(X+M+1)^2+(M-1)^2+(M+2N)^2=0 有实根所以(M-1)^2+(M+2N)^2<=0 所以只有M=1。M+2N=0得，M=1,N=-1/2
