Y=4X,
X1X2=P^2/4=4/4=1,
点OB是RT三角形QBF斜边QF中线
所以,OQ=OF=OB=P/2=1
B(X2,Y2,)
(X2)^2+(Y2))^2=1,(Y2))^2=4X2
(X2)^2+4X2=1
X2=√5-2
X1=1/X2=1/(√5-2)=√5+2
lx1-x2l=1(√5+2)-(√5-2)l=4
lx1-x2l=4
AF=x1+p/2 ,BF=x2+p/2
AF-BF=(x1+p/2 )-(x2+p/2)=lx1-x2l
AF-BF=lx1-x2l
AF-BF=4
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