Here is what I was given in the problem: A 0.27 kg mass is suspended on a spring that stretches a distance of 4.9 cm. It is then pulled downward an addtional distance of 12.5 cm and released. Find the displacement from the equilibrium position of the mass (in cm) after 0.42 sec. Count up as positive and g=9.81m/s^2. I figured out the spring constant (k=54.06 N/m) and the angular velocity (14.15 s^-1). I then entered the two values I had just found into the displacement equation [x at(t=0.42 s)=A cos (wt)] and got (-12.43 cm). That was wrong. The answer is (-11.78 cm). What did I do wrong? I tried the equation several different ways and got the same answer every time and it was the wrong one. Thanks so much for taking the time to help me.