因为p在直线AB上,所以,BP的斜率=AP(1-y)/(1-2)=(1-5)/(1-x) (1)式因为向量AP的模=2向量BP的模所以根号(1-5)^2+(1-x)^2=4(1-y)^2+4(1-2)^2化简得12=4(1-y)^2-(1-x)^2 (2)式由（1式得）（1-X）=4/(1-y)代入（2）式12=4...