Consider the expression −2 + 5a + b + 2a − 5b. which term can be combined with 5a because they are like terms? –2 b 2a –5b

Like terms will have exactly the same variables

so 5a and 2a are like terms

examples :
3b and 4b are like terms
3b and 4a are not like terms
2a^2 + 3a^2 are like terms
2a and 3a^2 are not like terms
3ab and 4ba are also like terms...even though the variables are switched
6b^2a and 6a^2b are not like terms

What do you mean by that?

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