Question 920123
(a) cos 11π/6= √3/2
 (b) cos(−11π/6) =  √3/2  cos(-θ) = cos (θ)
 (c) cos 17π/6 = cos (17π/6) = cos(5π/6 + 2π ) =  cos(5π/6) =  -√3/2

(cosx, sinx) Unit Circle Summary for Your reference
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