Find all points on the graph of the function f(x) = 2cos(x) + cos(x)^2 at which the tangent line is horizontal. I found the derivative to be -sinx(cosx + 2).
Find all points on the graph of the function f(x) = 2cos(x) + cos(x)^2 at which the tangent line is horizontal. I found the derivative to be -sinx(cosx + 2). Mr F says: This should be -2sinx(cosx + 1)
Now solve $\displaystyle -2\sin x (\cos x + 1) = 0$.