When mixing colors of light, why does combining a secondary color with its complementary color give white light?

Question

I can't find the answer in my book, please help!

Answer 1

well, if you buy into the fact that
red+green+blue = white
then the complement of any secondary color is the unused primary color.

Answer 2

unit 5 lesson 4 color (connexus)

1) red and yellow
2) complementary
3) complementary
4) split complementary
5) anger and war