初三數(shù)學(xué)平方根、立方根講義三

1、專業(yè)好文檔環(huán)球雅思學(xué)科教師輔導(dǎo)教案 年 級：初三 輔導(dǎo)科目：數(shù) 學(xué) 學(xué)員姓名： 學(xué)科教師：鞏慶偉授課類型t（平方根）t（立方根）t(平方根與立方根的運用與估算)星級授課日期及時段2013-11-16 10：10-12：10教學(xué)內(nèi)容課前小測試：a12345678910a2a11121314151617181920a2a12345678910a3t-平方根1、 如果一個數(shù)x的平方等于a，即，那么這個數(shù)x就叫做a的平方根，也叫做a的二次方根。2、表示方法：一個正數(shù)a的正的平方根用符號“”表示。a叫做被開方數(shù)2叫做根指數(shù)，正數(shù)a的負(fù)的平方根用符號“” 表示，兩個平3、算術(shù)平方根：如果一個正數(shù)x的平方等

2、于a，即，那么這個正數(shù)x就叫做a的算術(shù)平方根，記為“”。4、 平方根性質(zhì)：1）一個正數(shù)有兩個平方根，它們互為相反數(shù)；0有一個平方根，它是0本身；負(fù)數(shù)沒有平方根。2）雙重非負(fù)性。例1、如果，那么x_；如果，那么_例2、若，則（ ）a. b. c. d. 例3、若一個正數(shù)的平方根是和，則，這個正數(shù)是 ；例4、的最小值是_，此時的取值是_例5、求下列各式中的x. (1) x2=16 (2) 練習(xí)：1、的平方根是_，的算術(shù)平方根是_，的算術(shù)平方根是 ；2、若正數(shù)的算術(shù)平方根比它本身大，則（ ）a. b. c. d. 3、的算術(shù)平方根是2，則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） 小結(jié)：t-立方根1、 立方根：如果一個數(shù)x的立方等于a，即，那么這個數(shù)x就叫做a的立方根2、表示方法：如果x3a，那么x叫做a的立方根數(shù)a的立方根用符號表示，讀作“三次根號a”，其中a是被開方數(shù)，3是根指數(shù)（注意：根指數(shù)3不能省略）如下圖：3、性質(zhì)：例1、的立方根是 。 的立方根是 。 的立方根是 例2、若，則. 立方根是8的數(shù)是， 的立方根是。例3、求下列各式的值或x. （1）； （2）； （3）； （4）練習(xí)：1、若，則x；，則x，若，則x.2、求下列各數(shù)的立方根來源:21世紀(jì)教育網(wǎng)（1）729 （2）4 （3） （4）（5）

4、3、求下列各式中的x.21世紀(jì)教育網(wǎng)(1)125=8 (2)=216 (3) =2 (4)64小結(jié)：t-平方根與立方根運用與估算估算無理數(shù)的方法是：（1）通過平方運算，采用“夾逼法”，確定真值所在范圍；（2）根據(jù)問題中誤差允許的范圍，在真值的范圍內(nèi)取近似值。1、下列說法錯誤的是（ ）a、 b、 c、2的平方根是 d、的平方根是2、一個等腰三角形的兩邊長分別為和，則這個三角形的周長是（ ）a、 b、 c、或 d、無法確定3、估算下列數(shù)值并比較大小。練習(xí)：1、下列說法：一個數(shù)的平方根一定有兩個；一個正數(shù)的平方根一定是它的算術(shù)平方根；負(fù)數(shù)沒有立方根其中正確的個數(shù)有（ ）a，0個b，1個c，2個d，3

5、個2、若x2（3）2，y3（2）3，求x+y的所有可能值3、通過估算比較與2.5的大小。小結(jié)：課后作業(yè)：1的算術(shù)平方根是2的平方根是 它的算術(shù)平方根是 3如果一個數(shù)的平方根等于它的立方根，則這個數(shù)是4若x的立方根等于4，那么x的平方根是5已知的算術(shù)平方根等于8，則的立方根等于6的立方根等于7、計算：=；=；8.若x的算術(shù)平方根是4，則x=；若=1，則x=；9.若-9=0，則x=；若27+125=0，則x=；10當(dāng)x時，代數(shù)式2x+6的值沒有平方根；11.通過計算不難知道：，則按此規(guī)律，下一個式子是；12.求下列各式的值 13、估算下列值并比較大小 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