Can you give an example?Why does using a vector diagram and the centripetal acceleration formula give different values? (using exact values in both so it isn't rounding errors)
I think it might be because your doing the operations incorrectly. For example you can't just add or subtract two vectors the same way as numbers like 2+3. You need to consider what direction they're pointing and work out the resultant vectors magnitude appropriately using Pythagorus and what not.Can you give an example?
One possible reason may be that the formula you're using has implicit assumptions (e.g. uniform circular motion).