Question

prove that cos 100°+cos80°=0
plz fast

Answer 1

To prove cos 100°+cos80°=0
=> cos100 – cos80
=cos(90+10) – cos (90–10)
=sin 10–sin10
=0
Therefore, LHS= RHS
Hence proved

Answer 2

lhs=cos(100)+cos(80)

=cos(180-80)+cos(80)

=-cos(80)+cos80=0