Let

z1 = a + b i,     z2 = c + d i,

then,

z1 z2 = a + b i c + d i (1) = (a + i b)(c − d i) (c + d i)(c − d i) (2) = a c − a d i + b c i + b d c2 + d2 (3) = a c + b d c2 + d2 + b c − a d c2 + d2 i. (4)

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On 02 Mar 2025, 19:50.