Talk:Derivative of Cosine Function/Proof 5

Things to work on
You wanted some feedback, so here it goes.

1) Whenever you have something like == Theorem ==, the rule is to leave two empty lines before and one after.
 * Not quite. No extra blank line above the top == Theorem == of the page. --prime mover (talk) 16:16, 20 June 2020 (EDT)

2) Standalone equations look nicer when you put : in front.

3) When using begin-eqn template, please do not leave big gaps. The main use is to chop a long sequence (2 or 3) of (in)equalities. If you feel that mathematical statements are not immediately related, better not to write them in the same block. In your case, the very last equation should not be in begin-eqn.


 * Nope, put them all in the block. No problem with that at all. There's no hard and fast rules for this, just craft it as you see fit. If it looks like it works in an equation block, put it in. If it feels better as a string of equations separated by words of explanation, that too is okay.

4) Use latex commands, developed specifically for ProofWiki. In your case, things like need to be replaced either by \paren or \map. Please inform yourself how they are used.


 * I have been through and tidied it all up using the standard house style. --prime mover (talk) 16:16, 20 June 2020 (EDT)

5) Make sure that your proof actually proves the theorem. You left out a special case, but your theorem does not specify this constraint. Either find a way to extend your proof to be fully general or state in the theorem the assumption. The statement of the theorem should contain all nontrivial assumptions needed for the proof. If what you are trying to prove is beyond you, leave an appropriate template for missing proof.


 * The case where $\cos x = 0$ does indeed need to be addressed. --prime mover (talk) 16:16, 20 June 2020 (EDT)

Try to read other proofs. This is the fastest way to learn something. Also, do not rush with your proof. Start in your sandbox and gradually improve. Hope this helps. --Julius (talk) 15:28, 20 June 2020 (EDT)


 * Also, note the use of the "leadsto" symbol between lines to emphasise the flow of argument. --prime mover (talk) 16:16, 20 June 2020 (EDT)