How do you multiply $(15+ 13i ) ( 12- 9i )$ , assuming $i$ is an imaginary number?

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Answer 1 · 2017-03-08T05:31:40

$297+21i$

You multiply them just like real numbers, assuming that $i *i =-1$

$(15+13i)(12-9i)$

$=15*12+13i*12-15*9i-13i*9i$

$=180+156i-135i+117$

$=297+21i$

How do you multiply (15+ 13i ) ( 12- 9i )(15+ 13i ) ( 12- 9i ), assuming ii is an imaginary number?