jointly or together

To my ear, 'jointly' sounds like something from a legal document.

Nobody I know uses that word in ordinary conversation.

To be really practical about answering "When should I use 'jointly'?", I'd say "never".

CJ

Well, thank you Jim,
I am preparing myself for TOEFL and GRE. And I've heard that they care about an essay being formal. Do you have any suggestion? I don't like to be formal. But I guess that what is required.

Thank you for your time,

You don't have to be wordy to be formal. Wordiness and formality are two completely different things.

For the purposes of being "formal" for your essay, I would simply tell you to be sure to capitalize where necessary and not to use slang expressions.

CJ

Would you please explain what do you mean from capitalize?
And I changed the question, also. The "wordy" is omitted.

this is a sentence i wrote has capitalization mistakes.
This is a sentence I wrote does not have those mistakes.

CJ

I guess "had changed" would be better, because I had changed that before you answered. Am I right?

Yes, I do that, almost without any exception! I thought capitalization had another meaning too.
Anyway, thank you for your time.
I'm not a sycophant! But, honestly, you're a great teacher. I read your answers before.
Thanks.
And good luck.