Since cos 60° = 1/2 = sin 30°

and cos 30° = √3/2 = sin 60°

∴ cos 60° cos 30° — sin 60° sin 30° = (1/2) × (√3/2) - (√3/2) × (1/2)

= (√3/4) - (√3/4)

= 0