Multiply these as you would any binomial expressions, then replace i² with -1.
(4 -5i)·(2 +3i) = 4·2 +4·3i -5i·2 -5i·3i
... = 8 +12i -10i -15i²
... = 8+15 +2i
... = 23 +2i
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Your calculator may be able to do this problem for you.
