Nilai dari sin 75 derajat cos 15 derajat adalah

sin 75 cos 15
= [sin (45 - 30)] . [cos ( 45 - 30)]

= [sin 45 cos 30 - cos 45 sin 30] . [cos 45 cos 30 + sin 45 sin 30]

= [(1/2 √2).(1/2 √3) - (1/2 √2).(1/2)] . [(1/2 √2).(1/2 √3) + (1/2 √2).(1/2)]

= {(1/2 √2).[(1/2 √3) - (1/2)]} . {(1/2 √2) [(1/2 √3) + (1/2)]}

= (1/2 √2) {[(1/2 √3) - (1/2)] . [(1/2 √3) + (1/2)]}

= (1/2√2) { (1/2 √3)^2 - (1/2)^2 }

= (1/2√2) { (3/4)- (1/4) }

= (1/2√2) {1}

= 1/2 √2