由 aa2191943 於 星期二 七月 25, 2006 10:59 am
#ed_op#DIV#ed_cl##ed_op#DIV#ed_cl#圓外一點到圓的切線等長#ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl#所以: QP = QA = QB = AB/2#ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl#O#ed_op#SUB#ed_cl#1#ed_op#/SUB#ed_cl#A 與 O#ed_op#SUB#ed_cl#2#ed_op#/SUB#ed_cl#B 同時垂直 AB, 所以兩線平行#ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl#所以四邊形 AO#ed_op#SUB#ed_cl#1#ed_op#/SUB#ed_cl#O#ed_op#SUB#ed_cl#2#ed_op#/SUB#ed_cl#B 為梯形#ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl#AB = √[(O#ed_op#SUB#ed_cl#1#ed_op#/SUB#ed_cl#O#ed_op#SUB#ed_cl#2#ed_op#/SUB#ed_cl#)#ed_op#SUP#ed_cl#2#ed_op#/SUP#ed_cl#-(AO#ed_op#SUB#ed_cl#1#ed_op#/SUB#ed_cl#-BO#ed_op#SUB#ed_cl#2#ed_op#/SUB#ed_cl#)#ed_op#SUP#ed_cl#2#ed_op#/SUP#ed_cl#] = 2√3#ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl#所以 PQ = AB/2 = √3#ed_op#/DIV#ed_cl##ed_op#/DIV#ed_cl#