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lily
12-27-2013, 05:39 AM
SAT subject math 2 - Complex numbers

Which of the following is the result of the product (x-i)(x+i)?

(A) x^2
(B) x^2-1
(C) x^2+1
(D) x^2+2i
(E) x^2-2i

Thanks!

miranda
12-27-2013, 05:40 AM
For the imaginary unit i holds that i^2=-1

So, (x-i)(x+i)=x^2-(i)^2=x^2-(-1)= x^2+1

Therefore the correct answer is (C).

lily
12-27-2013, 05:41 AM
Thank you miranda!:D