题目内容
3x+4x=7x，3a+4b=7ab
×
×
．分析：（1）根据乘法分配律合并即可作出判断，（2）3a+4b=7ab，所含字母不同因此不能合并．
解答：解：3x+4x=7x，
3a与4b不能合并．
故答案为：×．
3a与4b不能合并．
故答案为：×．
点评：考查了用字母表示数，注意对运算律的灵活运用．
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