If cos x = - cos(pi/6) and pi/2<x<pi, what is the value of x?

  • just don't know how to work this out and would appreciate any help - thankyou!

1 Answer
Sep 30, 2017

#x = (5pi)/6#

Explanation:

On the unit circle x is in Quadrant 2.
#cos x = - cos (pi/6)# --> #x = pi - pi/6 = (5pi)/6#
Check by using trig table.
#cos (pi/6) = sqrt3/2# --> #- cos (pi/6) = - sqrt3/2#
Trig table shows: #cos ((5pi)/6) = - sqrt3/2#. Proved.