Q266 · Practice questionTechnology-freeComplex familiar6 marks
QUESTION 266 (6 marks)
Let . The angle addition identities may be used.
a)[6 marks]
Prove for all positive integers n by mathematical induction.
WORKED SOLUTION
6 marksPractice marking scheme
ANSWER
(a) De Moivre's theorem holds for every positive integer n.
Worked solution
(a) For , both sides are . Assume the statement is true for , where . Then
Thus the statement for k implies the statement for . By mathematical induction it holds for every positive integer n.
Equivalent justified methods accepted; respect any requested proof method.
Exact values unless specified. Sketches assessed by mathematical features, not artistic quality.
Part a: Verify the base case.
Part a: State the hypothesis for an arbitrary positive integer k.
Part a: Factor the st power and apply the hypothesis.
Part a: Expand real and imaginary parts correctly.
Part a: Use both angle addition identities.
Part a: State the induction conclusion and its domain.
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