From the following expression 

3ab, a²,b²,a,5ab,-2ab,2a²

the three terms are

Dear student, 
Your question seems to be incorrect /  incomplete . But assuming your question to be
From the following expression
3ab, a²,b²,a,5ab,-2ab,2a² 
the three like terms are:
here is the answer accordingly:
From the following expression
3ab, a²,b²,a,5ab,-2ab,2a² 
the three like terms are:

3ab,5ab-2ab

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