241圆(国外英语资料).docVIP

241圆(国外英语资料) The 241 round of.Txt love is colorful balloons, no matter how tough the color, can not afford a barbed tip gently. A first-class lover can not only make a woman love forever, but also love a woman all her life! The twenty-fourth chapter, circle 24.1 circles Guidance of learning Learn the basic nature of the circle, be sure to experience carefully round the following two basic characteristics: first, the circle is an axis of symmetry, the circle of any one diameter where the line is its axis of symmetry; two, the circle is a center of symmetry, the center is the center of symmetry of it, and a round angle the rotation around the center of any graphics, and graphics overlap (this feature also known as circle rotation invariance). Based on the two basic characteristics, can organically angle, line and arc together. Thinking integration Analytic emphasis 1. vertical path theorem Vertical theorem can be changed as follows: a line if meet: (1) Central; (2) perpendicular to the string; it follows: (3) bisects chord; (4) the bisection chord arc; (5) of the minor chord bisection. In fact, in a circle a straight line, as long as you have any two of these five conditions, it can launch the remaining three. In particular, the conclusion bisection chord (not diameter) diameter perpendicular to the string, and two bisection chord of the arc. The string is not diameter is its important condition, because a circle of any two diameters are always equal, but they are not necessarily vertical. [example 1] as shown in Figure 24 - 1 - 1, in the two concentric circles with O as the center, the chord AB of the great circle turns round in C and D two points Confirmation: AC = BD. Analysis on the circular graph often implies a lot of relations, such as OB, OC, OA connection, OD, we know that OA = OB, OC = OD, the triangle knowledge is not difficult to permit this, but taking into account the two round of string AB, CD on the same line, round and two the common center, so we ca