中四F4數學 圓的基本性質

c)

CE + EG + GD = CD = AB = 2AF = 2(6) = 12 cm
CE + EG + GD = 12 ... (1)

AF + FE + EB = AB = 12 cm
AF + FE + EB = 12 ... (2)

(1) - (2) :

(CE - EB) + (EG - FE) + (GD - AF) = 0
(CE - EB) + (√(OE² - OG²) - FE) + (GD - AF) = 0
(CE - EB) + (√(5² - 3²) - 4) + (6 - 6) = 0
(CE - EB) + (0) + (0) = 0
CE = EB , sub. into (2) :

AF + FE + CE = 12
6 + 4 + CE = 12
CE = 2 cm


圖片參考：http://i.imgur.com/aB4s4.jpg