YLL討論網

因為B為切點, 所以PB=PA, AO=BO.
但OE=6+2-4-2=2=EC. 所以易證OB=OC.
則AO=OC=BC => AC=2BC 且三角形ABC為一1:2:根號3的直角三角形.
所以角BCO=角BOC=60度. 角AOB=120度 =>角APB=60度 即APB為正三角形.
AB=AP=4根號3
DEC和PAC相似. EC:CA=ED:AP=1:4=根號3:4根號3
ED=根號3. BE=2根號3 所以BD=(2-1)根號3=根號3.

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