How do you multiply $(2+i)(2-3i)$ in trigonometric form?

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Answer 1 · 2017-10-21T17:13:59

$7-4i$

First, we have to know that
$i^1=i$
$i^2=-1$
$i^3=-i$
$i^4=1$

Then, we can expend the expression and simplify it with the above rule:

$(2+i)(2-3i)$
$=4-6i+2i-3i^2$
$=4-4i-3i^2$
$=4-4i-3(-1)$
$=4-4i+3$
$=7-4i$

It's the answer! Hope it can help you :)

How do you multiply (2+i)(2-3i) (2+i)(2-3i) in trigonometric form?