Question

Which of the following expressions is equal to 2x2 + 18 ?

Answer 1

Answer: Choice C. (2x - 6i)(x + 3i)

Work Shown:

2x^2 + 18

2(x^2 + 9)

2(x - 3i)(x + 3i) .... see note below

(2x - 6i)(x + 3i)

Note: I used the rule that a^2 + b^2 = (a - bi)(a + bi). I recommend FOILing out the right hand side to confirm the equation is true. You'll use the idea that i^2 = -1.