701*699
=(700+1)(700-1)
=700^2-1^2
=490000-1
=489999
99*101
=(100-1)(100+1)
=100^2-1^2
=10000-1
=9999
用平方差公式进行计算.（1）701*699 （2）99*101
701*699
=(700+1)(700-1)
=700^2-1^2
=490000-1
=489999
99*101
=(100-1)(100+1)
=100^2-1^2
=10000-1
=9999