Tentukan nilai cos 165°

cos(165°)
= cos(120° + 45°)
= cos(120°)cos(45°) - sin(120°)sin(45°)
= (-1/2)(√2/2) - (√3/2)(√2/2)
= -√2/4 - (√3√2)/4
= -√2/4 - √6/4
= (-√2 - √6)/4 
semoga benar dan membantu