nilai dari 4 sin 80°sin140°sin 200°

4 sin 8°.sin 140°.sin 200°

= 4 sin 80°.sin 40°.(-sin20°) 
= -4 (sin 80.sin 20) sin 40 
= -4 (-1/2) (cos 100-cos 60) sin 40 
= 2 (cos 100-1/2) sin 40 
= (2 cos 100.sin 40)-sin 40 
= (sin 140-sin 60)-sin 40 
= sin 40-(akar 3)/2-sin 40 
= -(akar 3)/2