The GCF of 9d and -18f is the value 9
This is because 9 is the largest factor that goes into 9d and -18f
We can factor each part like so
9d = 9*d
-18f = 9*(-2f)
allowing us to say...
9d - 18f = 9*d + 9*(-2f)
9d - 18f = 9(d-2f)
If we use the distributive property to distribute the 9 through to (d-2f), we end up with 9d-18f again. This is a good way to check the answer
Answer: 9(d-2f)
