(a-b)(a3+a2b+ab2+b3) = a4-b4
(a-b)(a4+a3b+a2b2+ab3+b4) = a5-b5
(a-b)[a(n-1) + a(n-2)b + a(n-3)b2 + ...+b(n-1)] = an-bn
a的次数加b的次数等于n-1
(a-b)(a3+a2b+ab2+b3) = a4-b4
(a-b)(a4+a3b+a2b2+ab3+b4) = a5-b5
(a-b)[a(n-1) + a(n-2)b + a(n-3)b2 + ...+b(n-1)] = an-bn
a的次数加b的次数等于n-1