You can enter input as either a decimal or as the opposite over the hypotenuse?
There are 2 different ways that you can enter input into our arc cos calculator
Method 1:
Enter a decimal between -1 and 1 inclusive. Remember that you cannot have a number greater than 1 or less than -1
Method 2:
Entering the ratio of the opposite side divided by the hypotenuse. (review arccos here)