A.\(\cos \left( {x + y} \right) = \cos x.\cos y - \sin x.\sin y\)
B.\(\cos \left( {x + y} \right) = \cos x.\cos y + \sin x.\sin y\)
C.\(\cos \left( {x + y} \right) = \cos x.\sin y + \sin x.\cos y\)
D.\(\cos \left( {x + y} \right) = \cos x.\sin y - \sin x.\cos y\)