Jika sudut a+b=phi/6,maka cos a?

π/6=30°=1/2√2
sin (A + B) = sin A cos B + cos A sin B
sin 30° = sin (30° + 0°)
= sin 30° cos 0° + cos 30° sin 0°
= 1/2 √2 ⋅ 1 + 1/2 √3 ⋅ 0
= 1/2 √2
Jadi cos A=30°
Smoga bermanfaat