Question 10 • MO-Algebra II A-CR
Step B replaces [cos(θ) + i sin(θ)]^k with cos(kθ) + i sin(kθ). That statement is the induction assumption, which says de Moivre’s theorem is true for n = k so it can be used to prove the case n = k + 1. Thus the correct choice is D, assumption (for n = k step).
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