berapa hasil dari cos 75° sin 45° =

sin x - sin y = 2.cos[(x+y)/(2)] . sin[(x-y)/(2)]
(sin x - sin y)/2 = cos[(x+y)/(2)] . sin[(x-y)/(2)] ... (1)

(x+y)/2 = 75
x + y = 150 ... (2)

(x-y)/2 = 45
x-y = 90 ... (3)

Dari pers 2 dan 3 kita eliminasi
x + y = 150
x - y = 90
--------------- +
2x = 240 -> x = 120

x + y = 150
x - y = 90
--------------- -
2y = 60 -> y = 30

Kembali ke pers 1, masukkan nilai masing masing x dan y
(sin x - sin y)/2 = cos[(x+y)/(2)] . sin[(x-y)/(2)]
(sin 120 - sin 30)/2 = cos75sin45
cos75sin45 = (1/2√3 - 1/2)/ 2
                    =( (√3 - 1)/2)/2
                    = √3 - 1