Use an appropriate identity to find the exact value of the expression.

cos (310) cos (50) - sin (310) sin (50)

We know that cos (a+b) = coa. cob-sia. sinb

cos (310+50) = coas (310). cos (50) - sin (310). sin (50)

1st) cos (310+50) cos (360) = 1

2nd) cos (310) = cos (50) and sin (310) = - sin (50)

3rd) 1 = cos² (50) - [-sin² (50) ]

1 = cos² (50) + sin² (50)

, which is 1