你好：2.9x9.9+0.29=0.29×99+0.29×1=0.29×（99+1）=0.29×100=29
2.9×9.9+0.29=2.9×9.9+2.9×0.1=2.9×（9.9+0.1）=2.9×10=29
2.9x9.9+0.29=2.9x9.9x2.9x0.1=2.9x(9.9+0.1)=2.9x10=29
(3-0.1)*(10-0.1)+0.29
