Question

when is 2cos x + 1 >0 , < 0 AND = 0

Answer 1

-1 < cos x < 1
-2 < 2cos x < 2
-1 < 2cos x + 1 < 3

For 2cos x + 1 > 0
0 < 2cos x + 1 < 3
-1 < 2cos x < 2
-1/2 < cos x < 1
-60 degrees < x < 120 degrees