There are several ways of joining the nine dots of a square using four straight lines. The easiest and most common method is by drawing a triangle and a diagonal line. You need a pencil and possibly a ruler to complete the task.
- Label the dots
Assign the dots numerical labels one through eight in a counter-clockwise manner from the top-left corner of the square. Label the dot at the center as nine.
- Draw the triangle
Using a pencil and a ruler, draw a straight line to join points three and five, passing through point four. Make another straight line from dot five to seven through six. Join dots two and eight with a straight line. Draw a straight projection line from point eight in the direction away from the square such that it's parallel to the line that joins points two and eight. Extend another straight line from point seven in the direction away from the square such that it's parallel to the line that joins five, six and seven. Ensure that these two projection lines meet each other. Draw another line of projection from dot three pointing away from the square such that it's parallel to the line that joins three, four and five. Draw the last projection line from dot two in the direction away from the square such that it is parallel to the line that joins two and eight. Extend these two projection lines to meet each other.
- Draw the diagonal
Draw a straight line that joins dots one and five through nine. This joins nine dots with only four straight lines.