(a3＋a-3)(a3－a-3)÷[(a4＋a-4＋1)(a－a-1)]
=[(a1+a-1)(a2-1+a-2)(a－a-1)(a2+1+a-2)]/
[(a4＋a-4＋1)(a－a-1)]
=[(a1+a-1)(a2-1+a-2)(a2+1+a-2)]/(a4＋a-4＋1)
=[(a1+a-1)(a4＋a-4＋1)]/(a4＋a-4＋1)
=(a1+a-1)
注：a3为a的立方，a-3为a的负三次方，a4为a的四次方，a-4为a的负四次方，a-1为a的负一次方,a2为a的二次方，a-2为a的负二次方！
因为：(a2-1+a-2)(a2+1+a-2)
=[(a2+a-2)-1][(a2+a-2)+1]
=(a4＋a-4＋1)