x²-2x+5=0
delta=(-2)²-4×1×5
delta=4-20
delta=-16
x1=(2-4i)/2. x2=(2+4i)/2
x1=1-2i. x2=1+2i
x²-2x+5=(x-x1)(x-x2)
=(x-1+2i)(x-1-2i)