99x99+199=(100-1)x(100-1)+(200-1)=10000-200+1+200-1=10000
99x99+(100+99)=99x(99+1)+100=9900+100=10000
99x99+199 =99x(99+1)+100 =99x100+100 =1000
=99+(99+1)+100 =99x100+100 =1000
99x99十(100十99)