Suppose we have a 9 column grid of numbers and we want to sum up the numbers on a T shape whose height and width is three numbers long. This problem is pretty easy with the solution being a linear function of the bottom of the T.
Now rotate the T by 90 degrees. For each rotation, work out the corresponding sum.
Someone (my slightly dumb teacher) gave me this problem and I found it kind of boring and trivial. Then they told me you can find the rotated cases by applying trig transformations (as they saw some student do it) but he doesn't know how exactly. I seriously doubt it, but am I missing something?