Answer:
1
Explanation:
The notion of "common factor" suggests that a factor is part of each term. Here, 1 is the only common factor.
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However, the expression can be factored as ...
x(2 +a) +3y(2 +a) = (x +3y)(2 +a)
If there were a common factor, it would appear outside the binomial factors. The value 1 is always present, but rarely shown.