SOLUTION: without using a calculator, find the smallest positive theta in degree and radian measure for which cos theta = - 1/2

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Question 941995: without using a calculator, find the smallest positive theta in degree and radian measure for which
cos theta = - 1/2
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
If the sign were not negative, then the rotating
vector would form a 30-60-90 triangle in the
1st quadrant. The cosine of 60 degrees is +1%2F2+
-----------------
As the vector rotates, the first time that the cosine
is +-1%2F2+ is when
+theta+=+120+ or
+theta+=+2%2Api%2F3+