This is not a trick: the cosine of the imaginary number 𝑖 is (e⁻¹ + e)/2. How on Earth does this follow from the definition of the cosine? No matte

This is not a trick: the cosine of the imaginary number 𝑖 is (e⁻¹ + e)/2. How on Earth does this follow from the definition of the cosine? No matte