Question

What is the product of these numbers?

Answer 1

Answer:

  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