Question

Which expression is the product of (x + 4i)(x − 4i)(x + 4)?

Answer 1

Answer= x³+4x²+16x+64

Expand the following:(x + 4 i) (x - 4 i) (x + 4)
(x - 4 i) (x + 4) = (x) (x) + (x) (4) + (-4 i) (x) + (-4 i) (4) = x^2 + 4 x - 4 i x - 16 i = -16 i + (4 - 4 i) x + x^2:
-16 i + (-4 i + 4) x + x^2 (4 i + x)
 | | | | x | + | 4 i
 | | x^2 | + | (4 - 4 i) x | - | 16 i
 | | | | (-16 i) x | + | 64
 | | (4 - 4 i) x^2 | + | (16 + 16 i) x | + | 0
x^3 | + | (4 i) x^2 | + | 0 | + | 0
x^3 | + | 4 x^2 | + | 16 x | + | 64:
Answer: x^3 + 4 x^2 + 16 x + 64

Answer 2

First multiply first 2 elements, so:
(x+4i)*(x-4i) =x^2-16i^2

Now: (x^2-16i^2)*(x+4)=x^3 + 4x^2 - 16xi^2 - 64i^2