(20 13? Harbin No.1 Model) Elective Course 4- 1: Selected lectures on geometric proof. As shown in the figure, AB is the diameter ⊙, the extension lines of chords BD and CA intersect at point E, and E
(20 13? Harbin No.1 Model) Elective Course 4- 1: Selected lectures on geometric proof. As shown in the figure, AB is the diameter ⊙, the extension lines of chords BD and CA intersect at point E, and EF is perpendicular to BA.
(1) Connect the CD, as shown in the following figure: From the theorem of circle angle, it can be concluded that ∠C=∠B and ∠BEC are * * common angles of △ABE and △CDE, ∴△ABE∽△CDE, ∴.DE=CE. AE∴BE？ DE+AC？ CE=CE2(3 points) (2)∵AB is the diameter ∵ O, ∴∠ ECB = 90, ∴CD= 12BE, FD= 12BE, so, e, f, c.