cos 195 cos 105 + sin 105 cos 75
= cos (195-105) + sin (105+75) [using angle sum and difference identities]
= cos 90 + sin 180
= 0 + 0
= 0
Therefore, cos 195 cos 105 + sin 105 cos 75 = 0
cos 195 cos 105 + sin 105 cos 75
= cos (195-105) + sin (105+75) [using angle sum and difference identities]
= cos 90 + sin 180
= 0 + 0
= 0
Therefore, cos 195 cos 105 + sin 105 cos 75 = 0