There is an ancient Greek mathematical story about the positional relationship between a straight line and a circle. Hippasus, an ancient Greek mathematician, showed Alexander the Great a magical mathematical tool-compass. He drew a circle and a straight line with a compass and asked Alexander the Great if he could draw a square equal to this circle with a ruler and compass. Alexander the Great thought it was a simple matter, so he picked up a ruler and compasses and began to draw squares. However, he soon found that he could not draw a square equal to a circle anyway. He tried to draw the sides of a square with a ruler, but the area of the square drawn in this way was always smaller than that of the circle. He also tried to draw the sides of a square with compasses, but the side length of the square drawn in this way was always greater than the diameter of the circle. Finally, Alexander the Great realized that he could not draw a square equal to a circle with a ruler and compasses. This problem became one of the three famous geometric problems in ancient Greek mathematics, and it was not solved until19th century. The positional relationship between a straight line and a circle is very complicated, and sometimes we need more advanced mathematical tools to understand and describe the relationship between them.