Nine dots, four straight lines

Question

Nine dots are arranged in a 3 by 3 square grid. 1. Draw four straight line segments, connected end to end (without lifting your pen), that pass through all nine dots. 2. Can it be done with three lines? With one?

Accepted Answer

Four lines: yes, if you let the lines extend beyond the square of dots. Three lines: yes, with very long lines. One line: yes, with a thick pen or by rolling the paper. Four lines. Put the dots at the points (0, 0) to (2, 2) with one unit between neighbours, y increasing upwards. 1. Start at the top-left dot (0, 2) and draw straight down through (0, 1) and (0, 0), continuing one unit below the grid to (0, minus 1). 2. From there draw diagonally up and to the right through (1, 0) and (2, 1), continuing to (3, 2), one unit beyond the right edge. 3. From there draw straight left along the top ro…

Nine dots, four straight lines

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