Find the exact value. Without using a calculator

Question

a) cos (-17pi/6)

b) sec (3pi/2)

Answer 1

17/6 = 2 5/6

that is twice around counterclockwise then -5pi/6
that is pi/6 below -x axis
and pi/6 = 180/6 = 30 deg
so 30 deg below -x axis
cos of that is -sqrt3/2

3 pi/2 is 180 + 90 = 270 or on -y axis
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