Question

(2 – 3i) and (4 + 3i)

The product of the two complex numbers above is a - 6i, where a is a constant. What is the value of a ?
(Note: i = -1)

Answer 1

Expanding the product gives

(2 - 3i) (4 + 3i) = 8 - 12i + 6i - 9i² = (8 + 9) + (6 - 12) i = 17 - 6i

so a = 17.