Answer
$25$
Work Step by Step
$(4+3\iota)$$(4-3\iota)$
Multiply using the FOIL method:
$=(4\times4)+(4\times-3i)+(3i\times4)+(3i \times-3i)
\\=16-12i+12i-9i^2
\\=16+9+0i
\\=25$
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