F.4MATHS QUESTION

Joint BT ,then △TBC ~ △ACT

we have AT / AB = AC / AT

8 / AB = (AB + 12) / 8

AB^2 + 12AB - 64 = 0

(AB - 4)(AB + 16) = 0

AB = 4 or AB = - 16 (rejected)

2009-03-08 13:22:58 補充：
The answer is (B) : 4 cm

2009-03-08 14:27:22 補充：
Corrections: △TBC ~ △ACT change to 『△ATB ~ △ACT』,
sorry for my mistake !