Question

Maths question on trigo

Answer 1

Answer:

sin(-300°)cos(-300°)+sin(-420°)cos(390°)

= -sin(300°)cos(300°)+sin(420°)cos(390°)

= -sin(2π-π/3)cos(2π-π/3)+sin(2π+π/3)cos(2π+π/6)

=sin(π/3)cos(π/3)+sin(π/3)cos(π/6)

=(√3/2)(-1/2)+(√3/2)(√3/2)

=(3-√3)/4