Question

For the first derivative of f(theta)=2cos(theta)+cos^2(theta),

I got
f'(theta)=-2sin(theta)+2cos(theta)-sin(theta)=0
After simplifying it, the book had
(-sin(theta))(1+cos(theta))=0 ... how did they get (1+cos(theta))??? the answers is prob really simple but i am stuck on it if anyone could kindly help. @Mathematics

Answer 1

Hello,

f(t)=2cos t +cos² t

f'(t)=-2sin t -2cos t*sin t
=-2sin(t)*(1+cos (t))
Maybe we must calculate f'(t)=0 ==>sin(t)(1+cos(t))=0