Patrick B. answered 07/13/19
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Math and computer tutor/teacher
-cos(pi/6) = -cos(30) = -sqrt(3)/2
(1/2)cos(-pi/3) = (1/2)(cos(-60)) = (1/2)(cos(300)) = (1/2)(1/2) = 1/4
(1) -sqrt(3)/8
(2) -sqrt(3)/2 * 4 = -2*sqrt(3)
(3) 3/4
(4) 1/1536