2 parallel lines with arrows on both ends to show that they extend indefinitely. The lines are slanting…
      
      2 parallel lines with arrows on both ends to show that they extend indefinitely. The lines are slanting…
      
      3 parallel lines with arrows on both ends to show that they extend indefinitely. The lines are slanting…
      
      3 parallel lines with arrows on both ends to show that they extend indefinitely. The lines are slanting…
      
      4 parallel lines with arrows on both ends to show that they extend indefinitely. The lines are slanting…
      
      4 parallel lines with arrows on both ends to show that they extend indefinitely. The lines are slanting…
      
      5 parallel lines with arrows on both ends to show that they extend indefinitely. The lines are slanting…
      
      5 parallel lines with arrows on both ends to show that they extend indefinitely. The lines are slanting…
      
      6 parallel lines with arrows on both ends to show that they extend indefinitely. The lines are slanting…
      
      6 parallel lines with arrows on both ends to show that they extend indefinitely. The lines are slanting…
      
      Illustration of a regular hexagon inscribed in a circle. This can also be described as a circle circumscribed…
      
      Illustration of a square, with diagonals drawn, circumscribed about a circle. This can also be described…
      
      Illustration of a square, with 1 diagonals drawn, circumscribed about a circle. This can also be described…
      
      Illustration of a square circumscribed about a circle. This can also be described as a circle inscribed…
      
      Illustration of a square inscribed in a circle. This can also be described as a circle circumscribed…
      
      Illustration of a square, with diagonals drawn, inscribed in a circle. This can also be described as…
      
      Illustration showing a circle with an inscribed and circumscribed quadrilateral.
      
      Any four-point on a curve of the second order and the four-side formed by the tangents at these points…
      
      Illustration of a parallelogram with diagonals AC and BD intersecting at point O.
      
      Illustration of a parallelogram with altitude and diagonal drawn.
      
      Illustration of a parallelogram with diagonals drawn to show they bisect each other.
      
      Illustration to show that when lines from two opposite vertices of a parallelogram to the midpoints…
      
      Illustration of a polygon with a diagonal drawn. A diagonal of a polygon is a line joining the vertices…
      
      A heraldic shield with a pursuer (purple) surface, shown by the diagonal lines stretching from the top-right…
      
      Quadrilateral with intersecting diagonals and segment connecting midpoints.
      
      Illustration to show that if the diagonals of a quadrilateral bisect each other, the figure is a parallelogram.
      
      Illustration to show that if the diagonals of a parallelogram are equal, the figure is a rectangle.
      
      A line with arrows on both ends to show that it extends indefinitely. The line is slanting up when read…
      
      A line with arrows on both ends to show that it extends indefinitely. The line is slanting down when…
      
      A line with arrows on both ends to show that it extends indefinitely. The line is slanting up when read…
      
      A line with arrows on both ends to show that it extends indefinitely. The line is slanting down when…
      
      Illustrations of a square with diagonal DB, BE cut off equal to BC, and EF drawn perpendicular to BD…
      
      Illustration of a trapezium, a quadrilateral having no two sides parallel. The diagonal is labeled in…
      
      Illustrations of a trapezoid with a line joining the midpoints of the diagonals.
      
      A heraldic shield with a green (vert) surface, represented by the diagonal lines drawn from the top…