Question

Find all points on the graph of the function f(x) = 2 cos(x) + (cos(x))2 at which the tangent line is horizontal. Consider the domain x = [0,2π).

[ , ] (Smaller x values)
[ , ] (Larger x values)

Answer 1

do you mean:
\[f(x)=2\cos x +\cos ^{2}x\]

Answer 2

i got
x=0 and x=pi
right or wrong?