Kuadran IV : 270° < α < 360° ( < α < 2π) sin (360° - α) = sin (-α) = -sin α cos (360° - α) = cos (-α) = cos α tan (360° - α) = tan (-α) = -tan α cotan (360° - α) = cotan (-α) = -cotan α secan (360° - α) = secan (-α) = -secan α sec (360° - α) = sec (-α) = sec α
Mari kita lihat soal tersebut. Tentukan nilai dari sin 110°! Jawab : sin 110° = sin (180 - 70)° = sin 70° = sin (90 - 20)° = cos 20° Jadi, nilai dari sin 110° sama dengan sin 70° atau cos 20°. Semangat!
Materi : Trigonometri
Kata Kunci : trigonomteri, pembagian, sudut
Pembahasan :
Dalam trigonometri, besar sudut α dibagi menjadi 4 kelompok, yaitu :
Kuadran I : 0° < α < 90° (0 < α < )
sin (90° - α) = cos α
cos (90° - α) = sin α
tan (90° - α) = cotan α
cotan (90° - α) = tan α
secan (90° - α) = sec α
sec (90° - α) = cosec α
Kuadran II : 90° < α < 180° ( < α < π)
sin (180° - α) = sin α
cos (180° - α) = -cos α
tan (180° - α) = -tan α
cotan (180° - α) = -cotan α
secan (180° - α) = secan α
sec (180° - α) = -sec α
Kuadran III : 180° < α < 270° (π < α < )
sin (270° - α) = -cos α
cos (270° - α) = -sin α
tan (270° - α) = cotan α
cotan (270° - α) = tan α
secan (270° - α) = -sec α
sec (270° - α) = -cosec α
Kuadran IV : 270° < α < 360° ( < α < 2π)
sin (360° - α) = sin (-α) = -sin α
cos (360° - α) = cos (-α) = cos α
tan (360° - α) = tan (-α) = -tan α
cotan (360° - α) = cotan (-α) = -cotan α
secan (360° - α) = secan (-α) = -secan α
sec (360° - α) = sec (-α) = sec α
Mari kita lihat soal tersebut.
Tentukan nilai dari sin 110°!
Jawab :
sin 110°
= sin (180 - 70)°
= sin 70°
= sin (90 - 20)°
= cos 20°
Jadi, nilai dari sin 110° sama dengan sin 70° atau cos 20°.
Semangat!