Suppose you drop a ball from a height of 10 feet. After the ball hits the floor, it rebounds to a height defined by the recursive formula an = 0.85an - 1. What is a1?

The motion of the ball as described above is an example of geometric sequence. A geometric sequence is that which the value of the succeeding terms share a common ratio. From the given, since the ball is dropped in 10 ft from the ground, this is the a1 or or the first term.