Just got the test back =(

Class just ended and I got my test back. The mark itself is not really low, but the problem is that I was too careless. For the first question, because it is what I do well, I got full mark for it (actually it is not hard lol). I also got full mark for the diagram in question 2. The problem is, for the third question, I lose 3 marks just because of 1 single careless mistake: during negation, ⇒ should be converted to ∧. I knew this, but then I forgot to do this. So for part a, c, and e, I lose the answer marks. Maybe this is good for me, at least this will make me never do the same mistake again. For the other mistakes, I figured out what I did wrong and I hope that I will learn from them.

For today's class, we learnt some proofing technique. Actually they are quite straight forward, and its good for me so far. For the proofing existence, at first I was thinking if we have to solve the equation before proofing, so that we will get 3 roots and this will show that the set is non-empty. I wanted to ask the professor about this after the class, but I was too focused on my test and then I forgot to ask =P. Maybe then I will ask the TA tmr in tutorial.