Hello, my function is x-2cos(x), derived to 1+2sin(x).

I need to find the local max and min points on the interval [0,2pi]

Solving for x (sinx=-0.5) I get -pi/6 which is outside of my interval. I therefore ignore that value. My textbook says the two values I need are 7pi/6 an 11pi/6.

My problem is I cant see how they calculated those two values.

Can someone please enlighten me !

Thanks kindly