Answer :
Use the unit circle.
-19pi/6 is the same as 3pi + pi/6
This means that it goes around the unit circle 3pi times and ends up at 7pi/6
So -19pi/6 is equivalent to 7pi/6.
Looking at the unit circle, cos(7pi/6) = -√3/2
-19pi/6 is the same as 3pi + pi/6
This means that it goes around the unit circle 3pi times and ends up at 7pi/6
So -19pi/6 is equivalent to 7pi/6.
Looking at the unit circle, cos(7pi/6) = -√3/2
