Which pair of complex numbers has a real-number product? O (1 + 2i) (8i)

0 (1 + 2i) (2 - 5i)

O (1 + 2i) (1 – 2i)

O (1 + 2i)(4i)

(1 + 2i)(1 - 2i)

Step-by-step explanation:

Multiplying a complex number and its conjugate results in a real number.

Thus

1 + 2i and 1 - 2i are conjugates

(1 + 2i)(1 - 2i) ← expand using FOIL

= 1 - 2I + 2I - 4I² [ note i² = - 1 ]

= 1 - 4(- 1)

= 1 + 4

= 5 ← a real number

answer:  

123455421

step-by-step explanation: easy

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