what is y?

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Suppose a weight is attached to a spring and bobs up and down, exhibiting symmetry. Suppose the graph of the displacement function is shown in the graph below, where the values on the :1:- axis represent the time in seconds and the y-axis represents the displacement in inches. Give the equation that models the vertical displacement of the weight on the spring. Enclose arguments of functions in parentheses. For example, sin (2 * :13) . Include a multiplication sign between symbols. For example, a * 7r