When I solve cos(3t)=0 for t, I get this:

t = (2 * ?n2 - 1) * pi / 6

Anyone know what the symbol is where I put the "?". I can't decipher it, or what it's supposed to represent.

if you clear your calculator's memory and try it again you will get ?n1 and not ?n2

this is the calculator's way of keeping track of how many of the ? it has given you when solving equations

that symbol just means that

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Using elementary concubinary logic, you can easily show that the flumex is both semi-dependent and, even more importantly, quasi-invariant