** Using WeBWorK **

The precedence situations is a but complicated. The precedences listed in the Context/Default.pm file are not actually the ones used in WeBWorK. They were experimental ones that I was using to try to make things like sin 2x produce sin(2*x) rather than sin(2)*x (which is why the function precedence is slightly lower than multiplication). It's also the reason that there are definitions for ' *', '* ', ' /', and '/ ', since spacing made a difference in that setting (e.g., sin 2x / 3 was parsed as sin(2*x)/3 while sin 2x/3 was sin(2x/3).

This turned out to be too complicated, and since it didn't correspond to the original WeBWorK parser (now long retired, but still in use when mathObjects were developed), I added the ability to switch all the precedences to match the original WeBWorK parser. That is done by the usePrecedence() call at line 268. That method is defined here. So the actual precedence of function application is 7.5, and of multiplication and division is 3 (while negation is precedence 6, as you indicate).

On the other hand, the function precedence is really only used for function application where the argument is not contained in parentheses, like sin x, as sin(x) is parsed without the need of precedence values. Since functions are always displayed with parentheses, the precedence of 7.5 is really meaningless, as you indicate. So parentheses around functions are controlled by a separate parentheses, the parenPrecedence, which is set to 5 by default, as you point out. Since 6 is bigger than 5, the unary minus shows parentheses for -[sin(x)] to make it absolutely clear what is being negated, as you note.

If you don't want these to show, you can change the function application's parenthesis precedence:

Context()->operators->set(fn => {parenPrecedence => 6.5});

This will display -sin(x) rather than -[sin(x)], but still show [sin(x)]^2 rather than sin(x)^2 (the precedence of ^ is 7).

So long story short, you can change the parentheses with the line above.