An object is attached to a coiled spring. The object is pulled down (negative direction from the rest position) 7 centimeters, and then released. Write an equation for the distance d of the object from its rest position, after t seconds if the amplitude is 7 centimeters and the period is 8 seconds. The equation for the distance d of the object from its rest position is]. (Type an exact answer, using it as needed. Use integers or fractions for any numbers in the equation.)