论文部分内容阅读
1遇有半径作切线,与半径垂直于外端 当题中的图形内有半径(或直径)时,可过半径(或直径)的外端作圆的切线,则这条切线垂直于经过切点的半径。这对证明题会增加新的条件。例1 已知:如图1,在⊙O中,OA⊥OB,在OB上任取一点E,AE交⊙O于点D,过D作切线DC交OB的延长线于点C,求证CD=CE. 略证过点A作⊙O的切线AF,那么AF⊥OA,又因为OA⊥OB,于是得到AF∥OB,∠CED=∠FAD,又由CD于⊙O相切于点D,得到∠CDE=∠FAD,故可得出结论。
1 If a radius is used as a tangent, and the radius is perpendicular to the outer end, the radius of the graph (or diameter) may be used. If the outer radius of the radius (or diameter) is used as the tangent of the circle, the tangent is perpendicular to the tangent. The radius of the point. This will add new conditions to the proposition. Example 1 Known: As shown in Figure 1, in ⊙O, OA⊥OB, take any point E on OB, AE intersect point O at point D, pass D to make tangent DC cross OB extension line at point C, verify CD= CE. Slightly verify that point A is the tangent AF of ⊙O, then AF⊥OA, and because OA⊥OB, then get AF∥OB, ∠CED=∠FAD, and then CD is tangent to point D at point D. ∠CDE=∠FAD, so it can be concluded.