Factoring trinomials?

When factoring a trinomial, your trying to find a common factor but what if one number is negative and the other is positive how do you know if the factor is negative or positive. for example 2x+6x-8
Update: no what i meant was 2 goes into all of them but the 8 is negative does that mean that -2 is the common factor or is it still 2?
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