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Gilbert Strang, Calculus, 3rd edition (Wellesley-Cambridge Press; MIT OpenCourseWare RES.18-001) §9.4 Complex Numbers, #30 · Complex Numbers · Polar form

Show that … and find a similar formula for

Show that $cos θ = \frac{1}{2} (e^{i θ} + e^{- i θ})$ and find a similar formula for $sin θ$ .

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Gilbert Strang, Calculus, 3rd edition (Wellesley-Cambridge Press; MIT OpenCourseWare RES.18-001) · §9.4 Complex Numbers, #30

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