Answer:
[tex]\displaystyle 45[/tex]
Step-by-step explanation:
[tex]\displaystyle (6 + 3i)(6 - 3i) = 36 - 9i^2 = 36 - 9[-1] = 36 + 9 = 45[/tex]
Extended Information on the Complex Number System
[tex]\displaystyle \sqrt{-1} = i \\ -1 = i^2 \\ -i = i^3 \\ 1 = i^4\:[Any\:multiple\:of\:four][/tex]
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