There is an identity of sin(2pi-x) = -sin(x) and cos(2pi-x) = cos(x). This is what we are going to use.
(7pi/6) = (2pi)-(pi/6)
Therefore:
1) sec(7pi/6) = 1/cos(2pi-(pi/6)) = 1/cos(pi/6) = 2sqrt(3)/3
2) cos(7pi/6) = cos(pi/6) = sqrt(3)/2
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