Mnożenie liczb zespolonych

$z = z_1 z_2 = (a_1 + ib_1)(a_2 + ib_2) = a_1a_2 + i^2b_1b_2 + i(a_1b_2 + b_1a_2) = (a_1a_2 - b_1b_2) + i(a_1b_2 + b_1a_2)$