Don't know how to do 9 and 10. Please help!

9. [0/1 Points] DETAILS PREVIOUS ANSWERS SCALCET7 3.3.033. For what values of x does the graph of f have a horizontal tangent? (Use n as your integer variable. Enter your answers as a comma-separated list.) R(x) = x - 2 sin(x) x = (2n - 1)at + (2n - 1)n- coly X Need Help? Watch It 10. [-/1 Points] DETAILS SCALCET9 3.3.041.MI. A mass on a spring vibrates horizontally on a smooth, level surface as shown in the figure. Its equation of motion is x(t) = 4 sin(t), where t is measured in seconds and x in centimeters. Equilibrium position 0 x (a) Find the velocity and acceleration at time t. V (t ) = a(t) (b) Find the position, velocity, and acceleration of the mass at time t = 2x/3. a ( 2) In what direction is the mass moving at that time? 2 v 0, the mass is moving to the [left V