Complex NumbersHard

Question

If 2 cosθ = x + and 2 cos φ = y + , then

Options

A.xn + = 2 cos (nθ)
B.= 2 cos (θ - φ)
C.xy + = 2 cos (θ + φ)
D.none of these

Solution

(A) x = e y = e
xn + = 2 cosnθ
(B) = ei(θ - φ) + e - i(θ - φ) = 2 cos(θ - φ)
(C) xy + = 2cos(θ + φ)

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