Was he correct? Why or why not?
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Angle 7π/6 is π/6 below the negative x-axis in the 3rd quadrant. Its cosine will be -(√3)/2.
Angle 11π/6 is π/6 below the positive x-axis in the 4th quadrant. Its cosine will be (√3)/2.
The cosines have the same magnitude, but their signs are opposite each other. Jeremy was not correct.