Question

How do you express `cos( (5 pi)/6 ) * cos (( 11 pi) /12 )` without using products of trigonometric functions?

Answer 1

`P = cos ((5pi)/6).cos ((11pi)/12)`
Trig table of special arcs, and unit circle -->
`cos ((5pi)/6) = - sqrt3/2`
`cos ((11pi)/12) = cos ((- pi/12) + pi) = - cos (-pi/12) = - cos (pi/12)`
P can be expressed as:
`P = (sqrt3/2).cos (pi/12)`