Question

Heeeeelp
1)Cos100+cos80
2)sin103-sin77

Answer 1

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