Respuesta :

steffaniasierrag

Answer:

First, we use distributive property:

[tex](z+3i)(z-3i)=z^2-3zi+3zi-9i^2[/tex]

Now, remember that [tex]i^2=-1[/tex], then

[tex]z^2-3zi+3zi-9i^2=z^2-9(-1)=z^2+9[/tex]

Then,

[tex](z+3i)(z-3i)=z^2+9[/tex]

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