What is ?
Hint
The corresponding acute angle of (positive) is in the second quadrant.
Answer
What is cos (-2π)?
2π makes a full circle, touching the x-axis on the right-hand side.
1
The corresponding acute angle of (positive) is in the third quadrant.
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?
is 
in the second quadrant.
?
is 
in the third quadrant.
?
is 
in the third quadrant.
?
is 
in the second quadrant.