共查询到20条相似文献，搜索用时 203 毫秒
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新课程标准》中强调 :“所选择的教材应尽量来源于自然、社会与科学中的现象和实际问题” .因此 ,以其他学科知识为素材的中考数学题 ,近几年倍受命题者的关注 .现以中考题为例 ,分学科剖析 .1 与物理学科的渗透例 1 已知 ,二氧化碳的密度 ρ(kg/m3 )与体积V(m3 )的函数关系式是 ρ=9.9V .( 1)求当V =5m3 时二氧化碳的密度 ρ ;( 2 )请写出二氧化碳的密度 ρ随V的增大 (或减小 )而变化的情况 .( 2 0 0 4年南通市 )解析 ( 1)当V =5m3 时 ,ρ =9.9V =9.95=1.98(kg/m3 ) ;( 2 )因为密度 ρ与V成反比例 ,所以密度 ρ随体积V的增大而减小… 相似文献
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混合物的平均密度与混合前所用溶质与溶剂的质量、密度有关 ;二者在未发生化学变化或分子缔合时 ,总体积等于混合物中溶剂与溶质的体积之和 ,这时平均密度能用特定公式计算出 ,而溶质与溶剂质量的多少常用溶质质量分数表达 ,因此混合物平均密度与溶质的质量分数之间也存在着特定的关系 .设溶剂密度为 ρ1,质量为m1;溶质密度为 ρ2 ,质量为m2 ,混合物其平均密度为 ρ ,则ρ =m1+m2V1+V2=m1+m2m1ρ1+m2ρ2=(m1+m2 ) ρ1ρ2m1ρ2 +m2 ρ1. ( 1 )溶质的质量分数为M =m2m1+m2.由此得m1=m2 ( 1 -M)M . ( 2 )将 ( 2 )式代入 ( 1 )式中得 :ρ =ρ1… 相似文献
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直角坐标系与极坐标系存在较大的差异 .学生初学极坐标时 ,往往受思维定势的影响 ,容易忽视这两种坐标系的差异 ,从而导致解题失误 .本文把学习中易被忽视的几个注意点综述如下 ,希望引起同学们警觉 .1 注意极坐标的多值性例 1 在极坐标系中 ,点Ｐ(5 ,π3)和点Ｑ(ρ ,2θ) (ρ∈Ｒ ,0 <θ<π)表示同一个点 ,求点Ｎ(ρ ,θ) .错解 ∵ ρ =5 ,2θ=π3,∴ ρ=5 ,θ =π6 ,即点Ｎ的坐标是 (5 ,π6 ) .剖析 点的极坐标具有多值性 ,可以有无数种表示形式 ,即点 (ρ ,θ)可表示为 (ρ ,2ｋπ +θ) ,也可以表示为 (- ρ ,(2ｋ+ 1)π +θ) .上… 相似文献
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祁正红 《数理化学习(高中版)》2006,(17)
一、直接法例1已知f(x)=x2(x≥0)x(x<0),g(x)=x(x≥0)-x2(x<0),则x<0时,f[g(x)]为()(A)-x(B)-x2(C)x(D)x2解:当x<0时,g(x)=-x2<0,所以f[g(x)]=g(x)=-x2,选(B).求复合函数的解析式,先求内层函数,再求外层函数,另外,分段函数要注意变量的范围.二、换元法例2已知f(1-cosx)=sin2x,求f(x).解:令1-cosx=t则cosx=1-t,-1≤1-t≤1,所以0≤t≤2.所以f(t)=1-(1-t)2=-t2+2t(0≤t≤2)所以f(x)=-x2+2x(0≤x≤2)三、配方法例3f(x-1x)=x2+x12.求f(x).解:f(x-1x)=x2+x12=(x-1x)2+2,所以f(x)=x2+2.四、待定系数法例4已知f(x)=3x-1,f[h(x)]=g(x)=2x+3,h(x)为x… 相似文献
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让我们看下面两个问题及其解答 :问题 1 :已知函数 y =f (2 x)的定义域为[1 ,2 },求函数 y =f (log2 x)的定义域 .[1]原解 :令 u =2 x,因为 y =f (2 x)的定义域为 [1 ,2 ],所以 1≤ x≤ 2 ,2≤ u≤ 4,所以函数 y =f (u)的定义域为 [2 ,4],由 2≤ log2 x≤ 4得 4≤ x≤ 1 6 ,故函数 y =f (log2 x)的定义域为 [4,1 6 ]问题 2 :已知 f (x + 1 ) =3 x + 1 ,求f (x)原解 :令 t=x + 1 ,则 t∈ [1 ,+∞ ) ,所以 x =(t-1 ) 2 ,所以 f (t) =3 (t-1 ) 2 + 1 =3 t2 -6 t+ 4 ,所以 f (x) =3 x2 -6 x + 4 ,x∈ [1 ,+∞ ) .对以上两个问题及其解答 ,相信大… 相似文献
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范长如 《中学生数理化(高中版)》2005,(Z1)
一、反解时忽视了原函数的定义域例1求y=x2+4x+2(0≤x≤2)的反函数. 错解:因为y=-x1+4x+2=-(x-2)2+6(0≤x≤2),y∈[2,6],所以x=2±(6-y)~(1/2).则反函数为y=2±(6-x)~(1/2)(2≤x≤6). 上述解法在解x时,没有根据原函数的定义域对x进行合理取舍,应将x=2+(6-x)~(1/2)舍去.正确的反函数为y=2-(6-x)~(1/2)(2≤x≤6). 相似文献
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万阿英 《呼伦贝尔学院学报》2007,15(4):78-82
本文利用格林函数的正性和Krassnoselιskii不动点定理建立了周期边值问题u' ρ2u=f(t,u),u(0)=u(2π),u'(0)=u'(2π)和-u' ρ2u=f(t,u),u(0)=u(2π),u'(0)=u'(2π)的正解的存在性和多重性结果. 相似文献
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题 求函数 ｙ =-ｘｘ2 +2ｘ +2 的值域。解 ｘ2 +2ｘ +2 =(ｘ +1 ) 2 +1≥ 1 >0 ,函数定义域为Ｒ。下用△法解题。原式变为 ｙ ｘ2 +2ｘ +2 =-ｘ①两边平方并整理得ｆ(ｘ) =(ｙ2 -1 )ｘ2 +2 ｙ2 ｘ +2 ｙ2 =0②∵ｘ∈Ｒ ,∴△≥ 0 ,即 (2 ｙ2 ) 2 -4(ｙ2 -1 )·2 ｙ2 ≥ 0 ,即 -ｙ2 (ｙ2 -2 )≥ 0 ,亦即 ｙ2 -2≤ 0 ,∴ -2≤ ｙ≤ 2 ,故原函数的值域为 [-2 ,2 ]。解答错了 ,错在哪里 ?在用△法解题时 ,首先要求二次项系数 ｙ2 -1≠0 ,即 ｙ≠± 1 ,上面解法中应完整考虑 ｙ2 -1≠ 0且△≥ 0 ,这时解得 -2≤ｙ≤ 2且 ｙ≠± 1。又 ｙ =± … 相似文献
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20 0 0年 6月 1 4日1.A,B,C三人分别以不同的均匀速度跑马拉松 .B的速度比 A大 10 ,而 C的速度又比 B小 15 .如果A用时 3小时 7分 ,求 B,C的用时 .2 .解不等式 2 | x2 - 4| - 1≥ x.3.一直角三角形的内接圆的触点分斜边成长度 3cm与长度 4 cm的两部分 ,求直角三角形面积的精确值 .4 .给定正常数 a>0 ,定义函数 f:[0 ,5 ]→ R如下 :当 0≤ t≤ 1时 ,f(t) =at;当 1≤ t≤ 2时 ,f(t) =a;当 2≤ t≤ 3时 ,f(t) =a+ a(t- 2 ) 2 ;当 3≤ t≤ 5时 ,f(t) =- a(t- 5 ) .问 a取何值时 ,函数 f为随机变量 x的密度函数并对 a的这个值 ,计算 P({… 相似文献
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邱崇丙 《唐山师范学院学报》2014,(1):21-23
汉字的六书,《说文》对“转注”一类,语焉不详。后世学者提及转注,也仅限于许慎所举出的例字。《汉字例说》一文,作者从转注的角度综合考虑,对部分现代常用字作了分析,跟传统的解释有所不同。希望能抛砖引玉,互相切磋,以推进学术研究。 相似文献
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Rachel Zupek 《海外英语》2007,(11):40-41
我们绝大部分人都同意一件事情——我们喜欢金钱。但是你对金钱的喜欢之情足够到让你创立一份事业么?.财富通常被人忽视,主要在于人们不能真正了 相似文献
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《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献
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YANGShiguo 《重庆大学学报(英文版)》2004,3(1):86-88
The problem on the geometrc inequalities involving an n-dimensional simplex and its inscribed simplex is studied. Aninequality is established, which reveals that the difference between the squared circumradius of the n-dimensional simplex andthe squared distance between its circumcenter and barycenter times the squared circumradius of its inscribed simplex is not lessthan the 2(n-1)th power of n times its squared inradius, and is equal to when the simplex is regular and its inscribed siplex is atangent point one. Deduction from this inequality reaches a generalization of n-dimensional Euler inequality indicating that thecircumradius of the simplex is not less than the n-fold inradius. Another inequality is derived to present the relationship betweenthe circumradius of the n-dimensional simplex and the circumradius and inradius of its pedal simplex. 相似文献
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Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject. 相似文献
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GUO Bao-feng Xiao Da-wei 《重庆大学学报(英文版)》2005,4(3):129-133
Using virtual reality for interactive design gives a designer an intuitive vision of a design and allows the designer to achieve a viable, optimal solution in a timely manner. The article discusses the process of making the Virtual Reality System of the Humble Administrator＇s Garden. Translating building data to the Virtual Reality Modeling Language （VRML） is by far unsatisfactory. This creates a challenge for computer designers to do optimization to meet requirements. Five different approaches to optimize models have been presented in this paper. The other methods are to optimize VRML and to reduce the file size. This is done by keeping polygon counts to a minimum and by applying such techniques as object culling and level-ofdetail switching. 相似文献
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The awareness of individualism can be traced back to the period of American Revolution when the Declaration of Independence was produced.It expressed basic beliefs concerning freedom,equality,democracy,privacy and the relationship between people and government,which were exactly what the philosophy of individualism mostly dealt with at that time.This paper is to exploit the essence of individualism by analyzing the Declaration .The analysis enables us to reconsider its significance to the issue of America human rights and foreign policies. 相似文献
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Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities. 相似文献