X2+4Y2+2X-4Y+2
=(x^2+2x+1)+(4y^2-4y+1)
=(x+1)^2+(2y-1)^2
=0
x+1=0,2y-1=0
x=-1,y=1/2
X2+5Y2=1+5/4=9/4
X2+5Y2的平方根=±3/2