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How do you multiply #(4+5i)(4-5i)#?

1 Answer

Aug 31, 2016

We know that

#(a+b)(a-b) = a^2 - b^2#
and that

# i^2 = -1#

It follows

#(4 + 5i)(4 - 5i)#

#= 4^2 - (5i)^2#

#= 16 - (25i^2)#

#= 16 + 25#

#= 41#

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