No, it's not a thank-you note, it's a note a student wrote to me on a quiz.
The problem asks the students to dilate a given triangle by a scale factor of 3 and to graph both triangles. When doing a dilation on an x-y grid, this is most easily done by simply multiplying each of the original coordinates by the scale factor, which is exactly what this student did. Unfortunately, he plotted one of his points incorrectly, so his dilated figure (which should have been the same shape as the original, just larger) didn't look right.
He called me over during the quiz to tell me that he knew he'd made a mistake somewhere, but he couldn't figure out where. I told him that if he couldn't figure it out, he should write me a note telling me what he did know.
And man, what a great note. In case you can't read it, it says:
I can't figure it out but the prime coordinates B' & C' do not look right. I say this because in the original coordinates, B and C are not lined up vertically, but for some reason my prime coordinates for B' & C' are.
One of my new goals is to get more of my students to write me notes like this one.