I had several CS courses where writing something to the effect of "I don't quite know the answer this question (or don't have time to solve it), but the formula

I had several CS courses where writing something to the effect of "I don't quite know the answer this question (or don't have time to solve it), but the formulas / algorithms / bits of info I think are relevant are: x, y, z." On a difficult question this might get half credit.