江苏徐州市2017年-2018度第一学期八年级数学期中试题

..............................................9分РEF=BE—CFР∵BO平分∠ABC ∴∠EBO=∠OBC ∵EF∥BC∴∠EOB=∠OBCР∴∠EOB=∠EBO ∴EO=EB ...........................................10分Р 同理FO=FC ............................................11分Р∴EF=EO-FO=BE-CF ............................................12分Р25.(1)在Rt△ABC中,∴......................1分Р假设存在点P使得PA=PB,则PA=PB=2t,PC=4-2t,Р在Rt△BPC中,Р∴......................................3分∴..................................................4分Р(2)当点P在点C或点B处时,一定在△ABC的角平分线上,此时t=2或t=3.5秒;..6分Р点P在边AC上时,即点P在∠ABC的平分线上时,点P到AB的距离等于4-2t,∴..........................................8分Р∴..................................................9分Р点P在边BC上时,即点P在∠BAC的平分线上时,点P到AB的距离等于2t-4,Р∴.......................................11分Р∴..................................................12分Р综上,t=2或t=3.5或或