avl trees rotations question As you can see in this tree its unbalanced at the root with a balanced factor of $-2$. You can also perform a Right left rotation or a Right Right rotation. Which do you have to pick in this case?
Apparently, you want to rebalance the AVL tree. 

You can either do a simple left rotation or a right-left rotation. 

I prefer not to mention right-right rotation since that term is misleading and ambiguous.

You can visualize what is happening. Go to AVL tree visualization, a page created by David Galles. Insert 2, 1, 4, 3, 5 in that order. Now look closely when you delete 1.