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#