合并同类项
5x-2x+4x=
3a+5b-2a+8b=
-3ab-二分之三ab+5ab=
7x
a+13b
ab/2
5x-2x+4x=(5-2+4)x=7x
3a+5b-2a+8b=(3-2)a+(5+8)b=a+13b
-3ab-二分之三ab+5ab=(-3-2/3+5)ab=4/3ab