Question

Sin20+sin40-sin80=
a) -1 b) 1 c) 2 d) 0

Answer 1

$2 \sin( \frac{20 + 40}{2} ) \cos( \frac{20 - 40}{2} ) - \sin(80)$

=cos10- sin(90-10)

=cos10- cos10

=0

so answer is zero

D.