If $$P + Q + R = 60$$°, then what is the value of $$\cos Q \cos R (\cos P - \sin P) + \sin Q \sin R (\sin P - \cos P)$$?

A

$$\frac{1}{2}$$

B

$$\frac{\surd3}{2}$$

C

$$\frac{1}{\surd2}$$

D

$$\surd2$$