a)
[tex]x^2-4x+13=0\\x^2-4x+4+9=0\\(x-2)^2=-9\\x-2=\sqrt{-9} \vee x-2=-\sqrt{-9}\\x=2+3i \vee x=2-3i[/tex]
b)
[tex]x^2+2x+5=0\\x^2+2x+1+4=0\\(x+1)^2=-4\\x+1=\sqrt{-4} \vee x+1=-\sqrt{-4}\\x=-1+2i \vee x=-1-2i[/tex]
c)
[tex]x^2-6x+10=0\\x^2-6x+9+1=0\\(x-3)^2=-1\\x-3 =\sqrt{-1} \vee x-3=-\sqrt{-1}\\x=3+i \vee x=3-i[/tex]
