cos 75 derajat cos 15 derajat kurang sin 75 derajat sin 15 derajat

[tex] \cos {75}^{0} \cos {15}^{0} - \sin{75}^{0} \sin{15}^{0} \\ = \cos( {75}^{0} + {15}^{0} ) \\ = \cos {90}^{0} \\ = 0[/tex]