Question

How do you evaluate `cos (pi/6) cos (pi/3) - sin (pi/6) sin (pi/3)`?

Answer 1

Zero

Explanation:

Apply the trig identity:
cos (a + b) = cos a.cos b - sin a.sin b
#cos (pi/6)cos (pi/3) - sin (pi/3)sin (pi/6) = cos (pi/3 + pi/6) = = cos (pi/2) = 0#