that's right, Pythagoras IS high school stuff.

As for the 1/n sin x , the joke is that the student has cancelled the letter 'n' in the denominator with the 'n' in 'sin x', as if this latter 'n' was a variable itself, which it obviously isn't. - It's a letter in the word 'sin', not a variable by itself. No-one needs to go to university to see that. Then, the joke continues as we end up with the word 'six'.

By itself "1/n sinx" is meaningless; it must have been part of a larger question. The joke is how the student confused the second 'n'. The same goes for the idea of 'expansion'. People are supposed to learn the binomial expansion in high school - or at least the idea of 'expanding' a mathematical term.

So, I don't agree with you or Lee about high school maths, unless our standards are very different. -Well, so much for a hoped-for laugh out of all this.

- Anyway all of these mistakes could well have been deliberate: they're quite clever, really.