How do you multiply $(1+3i)(-4-7i)(6-5i)$ ?

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Answer 1 · 2016-10-10T19:46:43

You can convert them into polar form and multiply them that way but I think it is just as easy to use the F.O.I.L. method (twice):

Answer: $7 - 199i$

You can convert them into polar form and multiply them that way but I think it is just as easy to use the F.O.I.L. method (twice):

$(1 + 3i)(-4 - 7i)(6 - 5i) =$

$(1 + 3i)(-24 + 20i - 42i + 35i^2) =$

Use $i^2 = -1$

$(1 + 3i)(-24 + 20i - 42i - 35) =$

Combine like terms:

$(1 + 3i)(-59 - 22i) =$

$-59 - 22i - 177i - 66i^2=$

Use $i^2 = -1$

$-59 - 22i - 177i + 66=$

Combine like terms:

$7 - 199i$

How do you multiply (1+3i)(-4-7i)(6-5i)(1+3i)(-4-7i)(6-5i)?