1. â BPC+â BPE+â EPD=â CPD=180°ï¼èâ BPE=90°ï¼==>â BPC+â EPD=90°==>â PBC=â EPD
==>Rtâ³BPCâ½Rtâ³PED
å½På¨CDç延é¿çº¿ä¸æ¶ï¼ææPDæ¯Rtâ³PEFæè¾¹ä¸çé«ï¼ï¼Fæ¯PBåADç交ç¹ï¼ãæ
èâ BPC=â DEP
==>Rtâ³BPCâ½Rtâ³PED==>ED/PC=PD/BC==>y/x = (x-4)/4==>y = x(x-4)/4=x^2/4 - x ,(x>4).
2.å½DE=1æ¶ï¼è¥ç¹På¨CDç延é¿çº¿ä¸ï¼å¨æ2çå½æ°å
³ç³»ï¼y = x(x-4)/4ï¼å½y=1æ¶ï¼æx=2+2â2(å¦å¤ä¸ä¸ªæ ¹å°äº4ï¼æ¯å¢æ ¹ï¼èå»)
è¥ç¹På¨CDä¸ï¼æ ¹æ®1çç»è®ºï¼Rtâ³BPCâ½Rtâ³PED==>DE/PC=DP/BC==>1/x=(4-x)/4
==>(x-2)^2=0==>x=2==>Pæ¯CDçä¸ç¹ã
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