7) For what values of x does the graph of f have a horizontal tangent? f (x) =xV3+2cosx 8) Find the derivative of the function. a) f(0) = cos (sin 30) b) y = 2sec x 9) Find y" by implicit differentiation. (Simplify your answer completely.) x2 + 2y2 =2 10) Use logarithmic differentiation to find the derivative of the function. y =(cosx)