For finding GCF, just find the least number among them.
For example:
a.) 6x^2 - 9 find what number that can be divided to 6. In this case, it is 2 and 3.
You can't divide 9 by 2 so the answer in this equation would be 3.
b.) 2a^ 2 + 22a + 60 I's just the same method to use. In this case, we will use 2a^2. The factors that can be divided to 2 is (2,1). So we will choose 2 because it is the GCF of 2 and the equation is divisible by 2.
