Question

Heeeeelp
1)Cos100+cos80
2)sin103-sin77

Answer 1

$cos(100) + cos(80) = cos(180 - 80) + cos(80) = - cos(80) + cos(80) = 0 \ sin(103) - sin(77) = sin(180 - 77) - sin(77) = sin(77) - sin(77) = 0$