3 cos 75° dikali cos 15°

3 cos 75° cos 15°
= 3 cos (90-15)° cos 15°
= 3 sin 15° cos 15°
= 3/2 (2 sin 15° cos 15°)
= 3/2 (sin (15+15)°)
= 3/2 sin 30°
= 3/2 . 1/2
= 3/4