How do you simplify $(5-4i)(3+6i)$ ?

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Answer 1 · 2016-02-05T20:17:36

39 + 18i

distribute the brackets using FOIL

$(5-4i)(3+6i) = 15 + 30i - 12i - 24i^2$

[ remember that $i^2 = (sqrt-1)^2 = -1$ ]

$15+30i-12i + 24 = 39 + 18i$

How do you simplify (5-4i)(3+6i)(5-4i)(3+6i)?