Good Question

Matthew 26:39

[39] Going a little farther, he fell with his face to the ground and prayed, "My Father, if it is possible, may this cup be taken from me. Yet not as I will, but as you will."

If God only forknew about the crucifixion, then why did Jesus ask The Father "...if there was another way"?

It seems clear, in the asking, that The Father was able to change the circumstances, if, there was another way.

You cannot predetermine the future if all you can do is know the future. However, you can most definately forknow the future if you have predetermined it.

1 Corinthians 14:20

[20] Brothers, stop thinking like children. In regard to evil be infants, but in your thinking be adults.