If you mean the one where you have to draw through the 9 dots, arranged in a square, with 4 straight lines then this is how you do it. From 1 corner draw a line which extends past the 3rd dot on that side. Then go through the 2 dots in a line to a point diagonally opposite the extended line. Then back to the start point, and then diagonally across to the opposite corned. You end up with a right angled triangle, larger than the square, with a line cutting it in half and extending to the other diagonal. Confusing - I could show you in 2 seconds with a pencil & paper!