I think that this is an interesting situation. If you choose to keep Mathematics Extension 1, you will (if I understood correctly) end up with 10 units, that is, you will not have any backup units and the fact that your performance in Mathematics Extension 1 has so far been unfavourable could be an indication that you should reconsider keeping this subject because it would definitely count and in the event of unfavourable overall performance, this could pose a negative impact on your ATAR. Of course, unfavourable performance in one task is far from decisive and you definitely have a great chance to make a comeback and do well in Mathematics Extension 1 should you choose to keep it.

Additionally, if you choose to keep Mathematics Extension 1, you will gain the knowledge from this subject that is assumed from you in your chosen degree. This is assuming that Mathematics Extension 1 is treated as assumed knowledge and not as a prerequisite with a minimum result required (such as a minimum requirement of a band E3 in the case of USyd). In such a case, you will be good to go, regardless of the final result that you achieve in Mathematics Extension 1, because you would have completed the subject in the first place.

The option of dropping Mathematics Extension 1 means that you will end up with 11 units, providing you with 1 backup unit, which can halve the effect of unfavourable performance in another 2-unit subject in the event that this is the case (hopefully not). You seem to have a more positive attitude towards Visual Arts despite the fact that you do not enjoy the theory aspect. Based on this, it would be a good idea to wait and make a more informed decision once you have a mark for your first Visual Arts task. Generally speaking, you should keep the subject that you can perform better in.

While the option of dropping Mathematics Extension 1 means that you will not complete this subject, this does not mean that you will not have the assumed knowledge or be unable to study your chosen degree. You should be aware of two elements:

- A subject that is treated as assumed knowledge does not make it a prerequisite. In your case, this means that you can still study your degree without having completed Mathematics Extension 1, although it is recommended that you do take this subject as it will be assumed that you are already familiar with its concepts.
- You can complete a bridging course targeting Mathematics Extension 1, which is a short course that familiarises you with Mathematics Extension 1 concepts, allowing you to start your degree comfortably, similar to a student who completed Mathematics Extension 1.

I hope this helps!