Secant line point a "tangent line" and in no points an "exterior line". A "chord" of a circle is the line segment that joins two distinct points of the circle. A chord is therefore contained in a unique secant line and each secant line determines a unique chord. In rigorous modern treatments of plane geometry, results that seem obvious and were assumed (without statement) by Euclid in his treatment, are usually proved. For instance, "Theorem (Elementary Circular Continuity)": If formula_1 is a circle and formula_2 a line that contains a point that is inside formula_1 and a point that is outside of
Area of a circle wrong. Suppose that the area enclosed by the circle is less than the area "T" of the triangle. Let "D" denote the deficit amount. Circumscribe a square, so that the midpoint of each edge lies on the circle. If the total area gap between the square and the circle, "G", is greater than "D", slice off the corners with circle tangents to make a circumscribed octagon, and continue slicing until the gap area is less than "D". The area of the polygon, "P", must be less than "T". This, too, forces a contradiction. For, a perpendicular to the midpoint of