合并同类项。29×33+29×72-29×5=（33+72-5）×29=100×29=2900
29×33+29×72-29×5=29×(33+72-5)=29×100=2900
29x(33+72-5)=29x100=2900
=29×（33+72-5）=29×100=2900
