[tex]\bf \stackrel{\textit{difference of squares}}{(6+3i)(6-3i)}\implies (6)^2-(3i)^2\implies \stackrel{\textit{recall }i^2=-1}{36-(3^2 i^2)}\implies 36-(9\cdot -1) \\\\\\ 36+9\implies 45[/tex]
Step-by-step explanation:
6*6 - 6*3i + 6*3i -3i*3i
36-18i+18i-9i^2
36-9(-1)= 36+9= 45
