初三数学平方根、立方根讲义三

1、专业好文档环球雅思学科教师辅导教案 年 级：初三 辅导科目：数 学 学员姓名： 学科教师：巩庆伟授课类型t（平方根）t（立方根）t(平方根与立方根的运用与估算)星级授课日期及时段2013-11-16 10：10-12：10教学内容课前小测试：a12345678910a2a11121314151617181920a2a12345678910a3t-平方根1、 如果一个数x的平方等于a，即，那么这个数x就叫做a的平方根，也叫做a的二次方根。2、表示方法：一个正数a的正的平方根用符号“”表示。a叫做被开方数2叫做根指数，正数a的负的平方根用符号“” 表示，两个平3、算术平方根：如果一个正数x的平方等

2、于a，即，那么这个正数x就叫做a的算术平方根，记为“”。4、 平方根性质：1）一个正数有两个平方根，它们互为相反数；0有一个平方根，它是0本身；负数没有平方根。2）双重非负性。例1、如果，那么x_；如果，那么_例2、若，则（ ）a. b. c. d. 例3、若一个正数的平方根是和，则，这个正数是 ；例4、的最小值是_，此时的取值是_例5、求下列各式中的x. (1) x2=16 (2) 练习：1、的平方根是_，的算术平方根是_，的算术平方根是 ；2、若正数的算术平方根比它本身大，则（ ）a. b. c. d. 3、的算术平方根是2，则x_4、(1)若，其中6，8，求的值； (2)若22+2，其中

3、12，5，求的值5、 解方程 （1）4(x+1)2=8 （2） 小结：t-立方根1、 立方根：如果一个数x的立方等于a，即，那么这个数x就叫做a的立方根2、表示方法：如果x3a，那么x叫做a的立方根数a的立方根用符号表示，读作“三次根号a”，其中a是被开方数，3是根指数（注意：根指数3不能省略）如下图：3、性质：例1、的立方根是 。 的立方根是 。 的立方根是 例2、若，则. 立方根是8的数是， 的立方根是。例3、求下列各式的值或x. （1）； （2）； （3）； （4）练习：1、若，则x；，则x，若，则x.2、求下列各数的立方根来源:21世纪教育网（1）729 （2）4 （3） （4）（5）

4、3、求下列各式中的x.21世纪教育网(1)125=8 (2)=216 (3) =2 (4)64小结：t-平方根与立方根运用与估算估算无理数的方法是：（1）通过平方运算，采用“夹逼法”，确定真值所在范围；（2）根据问题中误差允许的范围，在真值的范围内取近似值。1、下列说法错误的是（ ）a、 b、 c、2的平方根是 d、的平方根是2、一个等腰三角形的两边长分别为和，则这个三角形的周长是（ ）a、 b、 c、或 d、无法确定3、估算下列数值并比较大小。练习：1、下列说法：一个数的平方根一定有两个；一个正数的平方根一定是它的算术平方根；负数没有立方根其中正确的个数有（ ）a，0个b，1个c，2个d，3

5、个2、若x2（3）2，y3（2）3，求x+y的所有可能值3、通过估算比较与2.5的大小。小结：课后作业：1的算术平方根是2的平方根是 它的算术平方根是 3如果一个数的平方根等于它的立方根，则这个数是4若x的立方根等于4，那么x的平方根是5已知的算术平方根等于8，则的立方根等于6的立方根等于7、计算：=；=；8.若x的算术平方根是4，则x=；若=1，则x=；9.若-9=0，则x=；若27+125=0，则x=；10当x时，代数式2x+6的值没有平方根；11.通过计算不难知道：，则按此规律，下一个式子是；12.求下列各式的值 13、估算下列值并比较大小 winger tuivasa-sheck, w

6、ho 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 against usa.both sides boast 100% records heading into the encounter but australia have not

7、 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 with eight.but it is recently named rugby league international federation player of the

8、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 league and rugby union after triumphing with the all blacks in 2011.id give every award

9、 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 associations 150th anniversary celebrations and will attend citys premier league match at c

10、helsea 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 was.uefa hasopened disciplinary proceedings against cskafor the racist behaviour of their

11、 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 toures complaint. in a statement the russian side added: we found no racist insults from f

12、ans 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 to be very calm - winds less than 2 mph, with no precipitation or humidity and limited c

13、loud 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 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airl

14、iners (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 feet ( then, i would assume, he will slowly step out onto something resembling an olymp

15、ic 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 history has repeated itself here - the last try they conceded was scored by englands josh

16、 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 on the sort of stuff that wins you tough, even contests - strong defence, especially on t

17、heir 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 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