勾股定理讲义

1、 新思敏教育小班辅导讲义 2014年3月8日教师耿慧静班级八年级（下）授课时间 10：00-12:00授课科目数 学授课课题勾股定理课型巩固教学目标 1、 知识目标：学会勾股定理以及逆定理；2、 能力目标：掌握勾股定理及其逆定理的应用；3、情感态度与价值观：熟练掌握实际问题中应用勾股定理。教学重点和难点1、 重点：学会勾股定理以及逆定理；2、 难点：理解并掌握勾股定理及其逆定理的应用。本章重要知识点1.勾股数 中，为正整数时，称，为一组勾股数记住常见的勾股数可以提高解题速度，如；等用含字母的代数式表示组勾股数：（为正整数）；（为正整数） ；（，为正整数）。2.勾股定理及其逆定理的应用勾股定理及

2、其逆定理在解决一些实际问题或具体的几何问题中，是密不可分的一个整体通常既要通过逆定理判定一个三角形是直角三角形，又要用勾股定理求出边的长度，二者相辅相成，完成对问题的解决常见图形：经典题型题型一：直接考查勾股定理 例.在中，（1）已知，求的长； 已知，求的长。题型二：应用勾股定理建立方程例.在中，于，已知直角三角形的两直角边长之比为，斜边长为，则这个三角形的面积为已知直角三角形的周长为，斜边长为，则这个三角形的面积为分析：在解直角三角形时，要想到勾股定理，及两直角边的乘积等于斜边与斜边上高的乘积有时可根据勾股定理列方程求解例.如图中，求的长分析：此题将勾股定理与全等三角形的知识结合起来例4.如

3、图，,分别以各边为直径作半圆，求阴影部分面积 题型三：实际问题中应用勾股定理例5.如图有两棵树，一棵高，另一棵高，两树相距，一只小鸟从一棵树的树梢飞到另一棵数的树梢，至少飞了题型四：应用勾股定理逆定理，判定一个三角形是否是直角三角形例6.已知三角形的三边长为，判定是否为，例7.三边长为，满足，的三角形是什么形状？题型五：勾股定理与勾股定理的逆定理综合应用例8.已知中，边上的中线，求证：练习题1. 下面几组数:7,8,9；12,9,15；m2 + n2, m2n2, 2mn（m，n均为正整数,mn）；,.其中能组成直角三角形的三边长的是( )a. b. c. d. 2. 三角形的三边长为,则这个

4、三角形是( ) a. 等边三角形 b. 钝角三角形 c. 直角三角形 d. 锐角三角形. 3已知一个直角三角形的两边长分别为3和4，则第三边长是（）a5 b25cd5或4已知rtabc中，c=90，若a+b=14cm，c=10cm，则rtabc的面积是（）a. 24cm2b. 36cm2 c. 48cm2 d. 60cm25直角三角形中一直角边的长为9，另两边为连续自然数，则直角三角形的周长为（）a 121 b120 c90 d不能确定abefdc第10题图6.已知，如图，长方形abcd中，ab=3，ad=9，将此长方形折叠，使点b与点d重合，折痕为ef，则abe的面积为（）a.6b.8c.1

5、0d.127. 四根小木棒的长分别为5cm，8cm，12cm，13cm，任选三根组成三角形，其中有 个直角三角形.8. 如图8，有一块直角三角形纸片，两直角边ac=6cm，bc=8cm，现直角边沿直线ad折叠，使它落在斜边ab上，且与ae重合，则cd的长为 9. 一只蚂蚁沿直角三角形的边长爬行一周需2秒，如果将直角三角形的边长扩大1倍，那么这只蚂蚁再沿边长爬行一周需 （ ）.（a）6秒 （b）5秒 （c）4秒 （d）3秒10. 我国古代数学家赵爽“的勾股圆方图”是由四个全等的直角三角形与中间的一个小正方形拼成的一个大正方形（如图1所示），如果大正方形的面积是25，小正方形的面积是1，直角三角形

6、的两直角边分别是a、b，那么 的值为 （ ）.（a）49 （b）25 （c）13 （d）1本次课后作业：主任签字: 新思敏教育总部winger tuivasa-sheck, who scored two tries in the kiwis 20-18 semi-final win over england, has been passed fit after a lower-leg injury, while slater has been named at full-back but is still recovering from a knee injury aggravated aga

7、inst usa.both sides boast 100% records heading into the encounter but australia have not conceded a try since josh charnleys effort in their first pool match against england on the opening day.aussie winger jarryd hayne is the competitions top try scorer with nine, closely followed by tuivasa-sheck

8、with eight.but it is recently named rugby league international federation player of the year sonny bill williams who has attracted the most interest in the tournament so far.the kiwi - with a tournament high 17 offloads - has the chance of becoming the first player to win the world cup in both rugby

9、 league and rugby union after triumphing with the all blacks in 2011.id give every award back in a heartbeat just to get across the line this weekend, said williams.the (lack of) air up there watch mcayman islands-based webb, the head of fifas anti-racism taskforce, is in london for the football ass

10、ociations 150th anniversary celebrations and will attend citys premier league match at chelsea on sunday.i am going to be at the match tomorrow and i have asked to meet yaya toure, he told bbc sport.for me its about how he felt and i would like to speak to him first to find out what his experience w

11、as.uefa hasopened disciplinary proceedings against cskafor the racist behaviour of their fans duringcitys 2-1 win.michel platini, president of european footballs governing body, has also ordered an immediate investigation into the referees actions.cska said they were surprised and disappointed by to

12、ures complaint. in a statement the russian side added: we found no racist insults from fans of cska. baumgartner the disappointing news: mission aborted.the supersonic descent could happen as early as sunda.the weather plays an important role in this mission. starting at the ground, conditions have

13、to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. the balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. it will climb higher than the tip of mount everest (5.5 mi

14、les/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. as he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.the balloon will slowly drift to the edge of space at 120,000

15、 feet ( then, i would assume, he will slowly step out onto something resembling an olympic diving platform.they blew it in 2008 when they got caught cold in the final and they will not make the same mistake against the kiwis in manchester.five years ago they cruised through to the final and so far h

16、istory has repeated itself here - the last try they conceded was scored by englands josh charnley in the opening game of the tournament.that could be classed as a weakness, a team under-cooked - but i have been impressed by the kangaroos focus in their games since then.they have been concentrating o

17、n the sort of stuff that wins you tough, even contests - strong defence, especially on their own goal-line, completing sets and a good kick-chase. theyve been great at all the unglamorous stuff that often goes unnoticed in the stands but not by your team-mates.it is as though their entire tournament

18、 has been preparation for the final.in johnathan thurston, cooper cronk, cameron smith and either billy slater or greg inglis at full-back they have a spine that is unmatched in rugby league. they have played in so many high-pressure games - a priceless asset going into saturday.the kiwis are a lot

19、less experienced but winning a dramatic match like their semi-final against england will do wonders for their confidence.they defeated australia in the four nations final in 2010 and the last world cup, and know they can rise to the big occasion.winger tuivasa-sheck, who scored two tries in the kiwi

20、s 20-18 semi-final win over england, has been passed fit after a lower-leg injury, while slater has been named at full-back but is still recovering from a knee injury aggravated against usa.both sides boast 100% records heading into the encounter but australia have not conceded a try since josh char

21、nleys effort in their first pool match against england on the opening day.aussie winger jarryd hayne is the competitions top try scorer with nine, closely followed by tuivasa-sheck with eight.but it is recently named rugby league international federation player of the year sonny bill williams who ha

22、s attracted the most interest in the tournament so far.the kiwi - with a tournament high 17 offloads - has the chance of becoming the first player to win the world cup in both rugby league and rugby union after triumphing with the all blacks in 2011.id give every award back in a heartbeat just to ge

23、t across the line this weekend, said williams.the (lack of) air up there watch mcayman islands-based webb, the head of fifas anti-racism taskforce, is in london for the football associations 150th anniversary celebrations and will attend citys premier league match at chelsea on sunday.i am going to

24、be at the match tomorrow and i have asked to meet yaya toure, he told bbc sport.for me its about how he felt and i would like to speak to him first to find out what his experience was.uefa hasopened disciplinary proceedings against cskafor the racist behaviour of their fans duringcitys 2-1 win.miche

25、l platini, president of european footballs governing body, has also ordered an immediate investigation into the referees actions.cska said they were surprised and disappointed by toures complaint. in a statement the russian side added: we found no racist insults from fans of cska. baumgartner the di

26、sappointing news: mission aborted.the supersonic descent could happen as early as sunda.the weather plays an important role in this mission. starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. the balloon, with c

27、apsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. it will climb higher than the tip of mount everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometer

28、s) and into the stratosphere. as he crosses the boundary layer (called the tropopause),e can expect a lot of turbulence.the balloon will slowly drift to the edge of space at 120,000 feet ( then, i would assume, he will slowly step out onto something resembling an olympic diving platform.they blew it

29、 in 2008 when they got caught cold in the final and they will not make the same mistake against the kiwis in manchester.five years ago they cruised through to the final and so far history has repeated itself here - the last try they conceded was scored by englands josh charnley in the opening game of the tournament.that could be classed as a weakness, a