199十99X99
=100十99十99X99
=100十99X(1十99)
=100十99X100
=100十9900
=1000
199+99×99
=100+99+99×99
=100+99×(1+99)
=100+99×100
=100+9900
=10000
199十99x99=100十99十99x99=100十99x(1十99)=100十9900=10000。
199+99x99
=199+(100-1)x99
=199+9900-99
=100+9900
=10000
(200+100*100)-1