When you are trying to simplify fractions.
A couple of problems. You need at least two numbers to find a GCF and the GCF is by definition positive.
You don't; you need at least two numbers to find a GCF.
You need at least two numbers to find a GCF.
You need at least two numbers to find a GCF.
You need at least two numbers to find a GCF.
You need at least two numbers to find a GCF.
You need at least two numbers to find a GCF. If that's 72 and 96, the GCF is 24.
You need at least two numbers to find a GCF.
You need at least two numbers to find a GCF. If that's 16 and 66, the GCF is 2.
You need at least two numbers to find a GCF.
You need at least two numbers to find a GCF.
You need at least two numbers to find a GCF.