<!--
/* Font Definitions */
@font-face
{font-family:宋体;
panose-1:2 1 6 0 3 1 1 1 1 1;
mso-font-alt:SimSun;
mso-font-charset:134;
mso-generic-font-family:auto;
mso-font-pitch:variable;
mso-font-signature:3 135135232 16 0 262145 0;}
@font-face
{font-family:"\@宋体";
panose-1:2 1 6 0 3 1 1 1 1 1;
mso-font-charset:134;
mso-generic-font-family:auto;
mso-font-pitch:variable;
mso-font-signature:3 135135232 16 0 262145 0;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{mso-style-parent:"";
margin:0cm;
margin-bottom:.0001pt;
text-align:justify;
text-justify:inter-ideograph;
mso-pagination:none;
font-size:10.5pt;
mso-bidi-font-size:10.0pt;
font-family:"Times New Roman";
mso-fareast-font-family:宋体;
mso-font-kerning:1.0pt;}
p.MsoListContinue, li.MsoListContinue, div.MsoListContinue
{margin-top:0cm;
margin-right:0cm;
margin-bottom:6.0pt;
margin-left:21.0pt;
text-align:justify;
text-justify:inter-ideograph;
mso-pagination:none;
font-size:10.5pt;
mso-bidi-font-size:10.0pt;
font-family:"Times New Roman";
mso-fareast-font-family:宋体;
mso-font-kerning:1.0pt;}
/* Page Definitions */
@page
{mso-page-border-surround-header:no;
mso-page-border-surround-footer:no;}
@page Section1
{size:612.0pt 792.0pt;
margin:72.0pt 90.0pt 72.0pt 90.0pt;
mso-header-margin:36.0pt;
mso-footer-margin:36.0pt;
mso-paper-source:0;}
div.Section1
{page:Section1;}
-->
设E、F出发后运动了t秒时,EF与半圆相切.
过点F作KF∥BC交AB于K.如图9—8.则
BE = t,CF=4-2t,EK = t-(4-2t)=3t-4,EF= BE+ CF= t+(4-2t)=4-t.
又∵EF= EK+FK,
∴(4-2t)=(3t-4)+2.
解得t=.
∵1<t<2,∴t=.
∴当t= s时,线段EF与半圆相切.
(3)答:当1≤t<2时,点P的位置不会发生变化.
证明:1≤t<2时,设E、F出发后运动了t s时,EF位置如图9—9所示,则
BE = t,AE=2-t, CF=4-2t.
∴=.
又∵AB∥DC,∴△AEP∽△CFP.
∴.
即点P的位置与t的取值无关.
∴1≤t<2时,点P的位置不会发生变化,且AP:PC的值是.