第一个是加号吧65+65x99=65x1+99x1=65x（99+1）=65x100=6500
65×65×99=(65×65)×(100-1)=4225×100-4225×1=422500-4225=418275
=4225*99=4225*（100-1）=4225*100-4225*1=422500-4225=418275
