You have____(probable) never heard of Amy Hayes, ____she is a most unusual woman. She never throws away things we____(need) any more. She has always thought about how these things____(put) to good use. She thinks that nothing is a waste. The windows and doors of her house come from old buildings around her town ____were pulled down. The top of ____is an old boat____(turn) upside down. And the gate is made ____rocks and old glass bottles. Amy isn't the only one who is ____(recycle). Jessica Wong uses old clothes to make bags. She ____(do) this for a few years. Her bags are cute and useful.

对于0和1之间的任一个数a，用计算器求出a²﹣1的结果b．再用计算器求出b²﹣1的结果c…随着运算次数的增加，你发现了什么？