There is a small ball connected to a light spring, which makes a simple harmonic vibration with amplitude A along the x-axis, and its expression is expressed by a cosine function. If t = 0, the motion state of the ball is:
(1) x。= -A
(2) The overbalance position moves in the positive x direction
(3) Move to the negative direction of x at x = A / 2
(4) After x = A / radical2, move to the positive direction of x.
Use the vector diagram method to determine the value of the corresponding primary phase and write the vibration expression.