变形得y^2-2y+1=-2，配方得(y-1)^2=-2，开根得y-1=√-2，移项得y=1±√2i
y^2 - 2y + 3 = 0判别式：(-2)^2 - 4*1*3 = -8 ..... 2√2*iy = (2 ± 2√2*i)/2 = 1 ± √2*i
