Jawab:

Pembahasan :

Dalam trigonometri, besar sudut α dibagi menjadi 4 kelompok, yaitu :

Kuadran I : 0° < α < 90° (0 < α < π/2)

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° (π/2 < 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 < 3π/2)

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° (3π/2 < 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

Rumus yang penting dalam trigonometri, yaitu :

1.  

2.  

Mari kita lihat soal berikut.

tan 65° = tan (90 - 25)° = cotan 25°

cos 65° = cos (90 - 25)° = sin 25°

tan 25° . tan 65° -  

= tan 25° . cotan 25° -  

= tan 25° .  - 1

= 1 - 1

= 0

Jadi, nilai dari tan 25° . tan 65° -  adalah 0.

Penjelasan:

Maaf Kalau Salah, Tolong Jadikan Jawaban Yang Terbaik/Tercerdas.

Thank You!!!