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A real cubic has roots 2 and 1 + 2i. What is its third root?
A1 + 2i
B-1 + 2i
C1 - 2i
D-1 - 2i
Answer & Solution
Correct answer: C. 1 - 2i
Non-real roots of a real polynomial come in conjugate pairs, so 1 + 2i forces the third root 1 - 2i.
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