nilai dari cos 140°-cos 100°/sin 140°-sin 100° adalah

(cos 140° - cos 100°) / (sin 140° - sin 100°) = ....

cos 140° - cos 100°
= - sin 50° - ( - sin 10° )
= sin 10° - sin 50°
= 2 cos ( (10° + 50°) / 2 ) sin ( (10° - 50°) / 2 )
= 2 cos 30° sin - 20°
= 2 × ½ √2 × - (sin 20°)
= - √2 sin 20°

sin 140° - sin 100°
= 2 cos ( (140° + 100°) / 2 ) sin ( (140° - 100°) / 2 )
= 2 cos 120° sin 20°
= 2 × ( ½ ) sin 20°
= sin 20°

(cos 140° - cos 100°) / (sin 140° - sin 100°)
= √2 sin 20° / sin 20°
= √2


Tambahan :
Cara diatas menggunakan rumus :
sin A - sin B = 2 cos ( (A + B) / 2 ) sin ( (A - B) / 2 )