题目

如图，等边三角形ABC的边长为6cm，点P自点B出发，以1cm/s的速度向终点C运动；点Q自点C出发，以1cm/s的速度向终点A运动．若P，Q两点分别同时从B，C两点出发，问经过多少时间△PCQ的面积是2cm2？ 答案：【答案】经过2s或4s△PCQ的面积是2cm2【解析】试题分析：设经过xs△PCQ的面积是2cm2，由题意可得QC=xcm，PC=（6-x）cm，根据锐角三角函数再求得PC边上的高为xcm，根据三角形的面积公式列出方程（6﹣x）×x=2，解方程即可.试题解析： 设经过xs△PCQ的面积是2cm2，由题意得（6﹣x）×x=2解得：x1=2，x2=4，答：经过2Learners of English, especially self-taught learners may have trouble in understanding speeches by native speakers. The following ways might help improve their listening ability. First of all, do things step by step. It is not good to listen to something beyond your level. Better choose a suitable course and start with the first book. Go on to the second book only after you are sure you understand the first one. Secondly, stick to one course of study. Don’t change books often. Never let your attention be attracted by another course just because it seems to be more “fashionable”.  Thirdly, listen to the English news program over the radio from time to time.  Better go through the news stories in the Chinese-language newspaper first. That will make it easy for you to understand the English news on the radio. Fourthly, if you have time, listen to some interesting stories in “Special English from the V.O.A. or other listening materials of the same level as that of your textbook”1.This is a piece of advice to learners of English on how to ______.A.improve their listening abilityB.read fastC.write better English and read fasterD.speak correctly2.If you want to understand the English news program on the radio, you should ______.A.read the Chinese-language newspaper step by stepB.read again and again the Chinese-language newspaperC.go through the Chinese-language newspaper firstD.be able to recite the Chinese-language newspaper3.The author advised that once you have taken up a course, you ______.A.should stick to itB.should begin with the last bookC.should take up other courses if they are more fashionableD.shouldn’t do anything else4.In this passage, V.O stands for ______.A.a bookB.a magazineC.a text-bookD.a radio station