What is the product of these numbers? (1 + 2i)(2 + i) 1 − 5i 1 + 5i 0 − 5i 0 + 5i

  0 + 5i

Step-by-step explanation:

Multiply these the way you would any binomials, then replace i² with -1.

  (1 +2i)(2 +i) = 1·2 +1·i +(2i)·2 +(2i)·i

  = 2 + i + 4i + 2i² . . . . . the partial products

  = 2 +5i -2 . . . . . . . . . . after replacement of i² = -1

  = 0 +5i

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step-by-step explanation: ; )