find the numbers conjugate
[tex]\begin{gathered} z=1+2i \\ \bar{z}=1-2i \end{gathered}[/tex]continue by making the product between both of them
[tex]\begin{gathered} (1+2i)\cdot(1-2i) \\ 1-2i+2i-4i^2 \\ 1-4(\sqrt[]{-1})^2 \\ 1-4(-1) \\ 1+4 \\ 5 \end{gathered}[/tex]according to this a=5 and b=0
