9999×9999+19999
=9999×9999+10000+9999
=9999×(1+9999)+10000
=9999×10000+10000
=10000×(9999+1)
=10000×10000
=100000000
9999x9999+19999
=9999x9999+9999+10000
=9999x(9999+1)+10000
=99990000+10000
=100000000
=9999×9999+10000+9999
=9999×(9999+1)+10000
=9999×10000+10000
=(9999+1)×10000
=10000×10000
=100000000
=(10000-1)*(10000-1)+20000-1
=100000000-20000+1+20000-1
=100000000