How do you expand factors that contain one or more plus-minus signs

Such as (x ± 2)(x ± 4).

(x ± 2)(x ± 4) = { x^2-6x+8, x^2+6x+8, x^2+2x-8, x^2-2x-8 }

Note: Using sadface's solution would give you eight possible answers;
x² + 4x + 2x + 8 .. = x² + 6x + 8 . ok
x² + 4x + 2x - 8 ... = x² + 6x - 8 .. n.g.
x² + 4x - 2x + 8 ... = x² + 2x + 8 . n.g.
x² + 4x - 2x - 8 .... = x² + 2x - 8 .. ok
x² - 4x + 2x + 8 ... = x² - 2x + 8 .. n.g.
x² - 4x + 2x - 8 .... = x² - 2x - 8 ... ok
x² - 4x - 2x + 8 .... = x² - 6x + 8 .. ok
x² - 4x - 2x - 8 ..... = x² - 6x - 8 ... n.g.

Then make all operations ±

Foil as always

x² ± 4x ± 2x ± 8