It is not possible to give a sensible answer to this question. The greatest common factor (GCF) refers to a factor that is COMMON to two or more numbers. You have only one expression in the question: 25a^2 - 100 is NOT two expressions.
The GCF is a^2.
The GCF is 5a.The GCF is 5a.
The GCF is 6.
The GCF is 9.
The GCF is 4.
The GCF is 30.
50
The GCF is 27.
The GCF is: 1
The GCF is 1.
The GCF is 5.
The GCF is 2.