A small toy attached to the end of a slinky (or spring) bobs up and down according to an equation of the form

*d* =

*a* cos(

*bt*). The motion of the toy starts at its highest position of 5 inches above its rest point, bounces down to its lowest position of 5 inches below its rest point, and then bounces back to its highest position in a total of 4 seconds. Write an equation that represents this motion.

Graph your equation from *t* = 0 seconds to *t* = 12 seconds.