共查询到19条相似文献，搜索用时 140 毫秒
1.
从一个例子谈起 已知△ＡＢＣ的三个内角Ａ、Ｂ、Ｃ满足 :Ａ Ｃ =2Ｂ ,ｓｅｃＡ ｓｅｃＣ =- 2ｓｅｃＢ ,求ｃｏｓ Ａ -Ｃ2 的值 .解 由Ａ Ｃ =2Ｂ ,得Ａ Ｃ =12 0° ,Ｂ =6 0° .∵ ｓｅｃＡ ｓｅｃＣ =- 2ｓｅｃＢ ,∴ ｃｏｓＡ ｃｏｓＣ =- 2 2ｃｏｓＡｃｏｓＣ ,2ｃｏｓ Ａ Ｃ2 ｃｏｓ Ａ -Ｃ2=- 2〔2ｃｏｓ2 Ａ -Ｃ2 - 1 ｃｏｓ(Ａ Ｃ)〕 ,即 4 2ｃｏｓ2 Ａ -Ｃ2 2ｃｏｓ Ａ -Ｃ2 - 32 =0 .因 - 324 <- 1,故解得ｃｏｓ Ａ -Ｃ2 =22 .1 关于解题思维表现的分析上例中 ,条件是三角形三内角的一个关系式和有关这些角的一… 相似文献
2.
裘良 《中学数学教学参考》2001,(10)
广义射影定理定理 在△ＡＢＣ中 ,ＡＤ是高 ,ＡＢ =ｃ,ＡＣ =ｂ.(1 )若Ｄ在边ＢＣ上 ,则ＡＤ2 -ＣＤ·ＢＤ =ＡＣ2-ＢＣ·ＣＤ =ＡＢ2 -ＢＤ·ＢＣ =ｂｃｃｏｓＡ ;(2 )若Ｄ在ＢＣ或ＣＢ的延长线上 ,则ＡＤ2 ＣＤ·ＢＤ =ＡＣ2 ±ＢＣ·ＣＤ =ＡＢ2 ＢＤ·ＢＣ =ｂｃｃｏｓＡ .证明 :(1 )当Ｄ与Ｂ或Ｃ重合时 ,等式显然成立 .当Ｄ在ＢＣ上时 ,如图 ,记∠ＣＡＤ =α ,∠ＢＡＤ =β ,则ｃｏｓＡ =ｃｏｓ (α β)=ｃｏｓαｃｏｓβ-ｓｉｎαｓｉｎ β=ＡＤｂ ·ＡＤｃ -ＣＤｂ ·ＢＤｃ=ＡＤ2 -ＣＤ·ＢＤｂｃ .∴ＡＤ2 -ＣＤ·ＢＤ =ｂｃｃ… 相似文献
3.
电教常用缩写术语释译单淑明ＡＢＣ：ＡｍｅｒｉｃａＢｒｏａｄｃａｓｔｉｎｇＣｏｍｐａｎｙ美国广播公司ＢＢＣ：ＢｒｉｔｉｓｈＢｒｏａｄｃａｓｔｉｎｓＣｏｒｐｏｒａｔｉｏｎ．英国广播公司ＡＥＣＴ：ＴｈｅＡｓｓｏｃｉａｔｉｏｎｆｏｒＥｄｕｃａｔｉｏｎａｌＣｏ... 相似文献
4.
命题 设Ｄ、Ｅ、Ｆ分别是△ＡＢＣ的边ＢＣ、ＣＡ、ＡＢ上的周界中点 ,且ＢＣ =ａ ,ＣＡ =ｂ,ＡＢ =ｃ ,ｓ=12 (ａ +ｂ +ｃ) ,△ＡＥＦ、△ＢＤＦ、△ＣＤＥ、△ＡＢＣ的面积分别记为△Ａ、△Ｂ、△ Ｃ、△ ,△ＡＢＣ的外接圆半径为Ｒ .则有 ∑(ｓ-ａ)△ Ａ=△22Ｒ.证明 :由三角形周界中点的定义知ｓ=ＡＢ +ＡＥ =ｃ +ＡＥ ,ｓ=ＡＣ +ＡＦ =ｂ +ＡＦ ,则ＡＥ =ｓ-ｃ,ＡＦ =ｓ-ｂ .又∵ｓｉｎＡ =ａ2Ｒ,ｓｉｎＢ =ｂ2Ｒ,ｓｉｎＣ =ｃ2Ｒ,∴△Ａ =12 ＡＥ·ＡＦ·ｓｉｎＡ=12 (ｓ-ｃ) (ｓ-ｂ)· ａ2Ｒ=ａ4Ｒ(ｓ-ｂ) (ｓ-ｃ) .故 (ｓ-ａ)△Ａ=… 相似文献
5.
两个重要的三角恒等式杨变清郭海萍ｃｏｓ（Ａ＋Ｂ＋Ｃ）＋ｃｏｓ（Ａ＋Ｂ－Ｃ）＋ｃｏｓ（Ａ－Ｂ＋Ｃ）＋ｃｏｓ（－Ａ＋Ｂ＋Ｃ）＝４ｃｏｓＡｃｏｓＢｃｏｓＣ……（＊）其正确性既可由左和差化积到右,也可由右积化和差到左。在（＊）中分别以π２＋Ａ、π２＋Ｂ、π２... 相似文献
6.
1 Ｉｎｔｒｏｄｕｃｔｉｏｎ Ａ ｇｅｎｅｒａｌｉｚｅｄｉｎｖｅｒｓｅｍａｔｒｉｘＰａｄ啨ａｐｐｒｏｘｉｍａｎｔ(ＧＭＰＡ)ｉｓｉｎｔｒｏｄｕｃｅｄｏｎｔｈｅｂａｓｉｓｏｆｓｃａｌａｒｐｒｏｄｕｃｔｏｆｍａｔｒｉｃｅｓｉｎＲｅｆ.[1].ＴｈｅｅｘｐｒｅｓｓｉｏｎｏｆＧＭＰＡｉｓｏｆｔｈｅｆｏｒｍｏｆｍａｔｒｉｘｎｕｍｅｒａｔｏｒａｎｄｓｃａｌａｒｄｅｎｏｍｉｎａｔｏｒ ,ｗｈｉｃｈｉｓｄｉｆｆｅｒｅｎｔｆｒｏｍｔｈａｔｏｆＢｏｓｅａｎｄＢａｓｕ[2 ] .Ａｓｃｏｍｐａｒｅｄｔｏｔｈｅｅｘｉｓｔｉｎｇｍａｔｒ… 相似文献
7.
SHI Yao ming XU Shi Yue CHEN Hang de 《上海大学学报(英文版)》1999,3(4):274-278
１ Ｉｎｔｒｏｄｕｃｔｉｏｎ Ｒｅｃｅｎｔｌｙ,ａｓｅｒｉｅｓｏｆｅｘｐｅｒｉｍｅｎｔｓｂｙＹａｃｏｂｙｅｔａｌ．［１］ａｎｄＢｕｋｓｅｔａｌ．［２］ｒｅｐｏｒｔｅｄｓｏｍｅｍｅａｓｕｒｅｍｅｎｔｓｏｆｅｌｅｃｔｒｏｎｔｒａｎｓｍｉｓｓｉｏｎｐｈａｓｅｉｎｒｅｓｏｎａｎｔｔｕｎｎｅｌｉｎｇｔｈｒｏｕｇｈａｑｕａｎｔｕｍｄｏｔ（ＱＤ）ｗｈｉｃｈｉｓｉｎｓｅｒｔｅｄｉｎｔｏｏｎｅａｒｍｏｆａｎＡｈａｒｏｎｏｖＢｏｈｍ（ＡＢ）ｒｉｎｇ．ＴｈｅｃｏｎｄｕｃｔａｎｃｅｔｈｒｏｕｇｈｔｈｅＡＢｒｉｎｇｗ… 相似文献
8.
1 Ｉｎｔｒｏｄｕｃｔｉｏｎ ＡＢ5 ｔｙｐｅｈｙｄｒｏｇｅｎｓｔｏｒａｇｅａｌｌｏｙｓｈａｖｅｂｅｅｎｉｎｔｅｎ ｓｉｖｅｌｙｉｎｖｅｓｔｉｇａｔｅｄｓｉｎｃｅｔｈｅｆｉｒｓｔｕｓｅａｓａｎｅｌｅｃｔｒｏｄｅｒｅｐｏｒｔｅｄｂｙＪｕｓｔｉｉｎ 1973[1] .ＴｈｅｃｏｍｍｅｒｃｉａｌＡＢ5ｅｌｅｃｔｒｏｄｅｓｕｓｅｍｉｓｃｈｍｅｔａｌ,ａｌｏｗｃｏｓｔｍｉｘｔｕｒｅｏｆｒａｒｅｅａｒｔｈｅｌｅｍｅｎｔｓ ,ａｓａｓｕｂｓｔｉｔｕｔｅｆｏｒＬａ ,ｗｈｉｌｅｔｈｅＢ5ｃｏｍｐｏｎｅｎｔｒｅｍａｉｎｓｐｒｉｍａｒ… 相似文献
9.
凸四边形面积公式的证明及推广 总被引：1，自引：0，他引：1
对△ＡＢＣ ,记ＢＣ =ａ ,ＣＡ =ｂ,ＡＢ =ｃ,ｓ=(ａ ｂ ｃ) /2 ,△为其面积 ,则有海伦定理 :Δ =ｓ(ｓ-ａ) (ｓ-ｂ) (ｓ-ｃ)。对上述定理 ,有熟知的推广 :定理 1 对圆的内接四边形ＡＢＣＤ ,若ＡＢ =ａ ,ＢＣ =ｂ ,ＣＤ =ｃ ,ＤＡ =ｄ ,ｓ=(ａ ｂ ｃ ｄ) /2 ,△是其面积 ,则Δ =ｓ(ｓ-ａ) (ｓ-ｂ) (ｓ-ｃ) (ｓ-ｄ)。当ｄ =0时 ,我们得到海伦定理。文 [1 ]给出了一个凸四边形的面积公式如下 :定理 2 对凸四边形ＡＢＣＤ ,若ＡＢ =ａ ,ＢＣ =ｂ ,ＣＤ =ｃ,ＤＡ =ｄ ,ｓ=(ａ ｂ ｃ ｄ) /2 ,四边形ＡＢＣＤ的一组对角和为 2ｕ ,△是其… 相似文献
10.
Ｄｅｆｉｎｉｔｉｏｎ ＬｅｔＷｂｅａｓｕｂｓｐａｃｅｏｆＭｎ(Ｃ) ,ｔｈｅｎ ｏｒｄｅｒｍａｔｒｉｘｓｐａｃｅｏｎｃｏｍｐｌｅｘｆｉｅｌｄ .ＩｆＡＢ =ＢＡ , Ａ ,Ｂ∈Ｗ ,ｔｈｅｎＷｉｓｃａｌｌｅｄａｃｏｍｍｕｔａｂｌｅｍａｔｒｉｘｓｐａｃｅ(ＣＭＳ)ｏｆＭｎ(Ｃ) . ＡｍｏｎｇａｌｌＣＭＳｏｆＭｎ(Ｃ) ,ｔｈｅｒｅｍｕｓｔｅｘｉｓｔａＣＭＳｗｉｔｈｍａｘｉｍａｌｄｉｍｅｎｓｉｏｎｓ,ｄｅｎｏｔｅｄｂｙＷ(ｎ)ｍａｘ,ａｎｄｔｈｅｍａｘｉｍａｌｄｉｍｅｎｓｉｏｎｓｂｙｄ(ｎ)ｍａｘ.Ｔｈｅｃｏｎｓｔｒｕｃｔｉｏｎ… 相似文献
11.
Ml0.7Mm0.3Ni3.7Co0.7Mn0.4Al0.2 nanocrystalline hydrogen storage materials are prepared by melt-spinning(MS).X-ray diffraction is used for the measurement of the nanocrystalline size.Compared to the electrode of polycrystalline alloys,the property of activation MH9metal hydride)electrode of the alloys with nanometer scale became worse and the inital discharge capacity decreased.It may be ascribed to the decrease of the total amount of rare earth metals and the increase of oxygen on the surface from the analysis of components of the alloys.After heat-treatment,the electrochemical performance of MH electrode of as-spun alloys could be improved,which could be attributed to the alleviation of the lattice strain. 相似文献
12.
The Mg-based hydrogen storage alloys Mg2Ni, Mg2Ni0.7Fe0.3 and Mgl.7Alo.3Ni were successfully synthesized by a two-step process （sintering and ball milling）. The crystal structure and microstructure were examined by X-ray diffraction, Scanning Electron Microscope and Malvern particle size analyzer. New phase appears in the tripe alloys doped with A1 and Fe, and the particle size ranges from 3μm to 5 μm. The electrochemical performance studies indicate that the partial substitution of AI for Mg, and Fe for Ni significantly improve the cycle life, reversibility of hydrogen absorption and desorption. The diffusion process is the control step in the electrode reaction of hydrogen storage alloys. 相似文献
13.
新型铁磁性材料的结构电磁特性及在配电变压器中的应用 总被引：1，自引：0，他引：1
文章系统地论述了新型铁磁性材料--铁基非晶、铁基大块非晶、铁基纳米晶、铁基大块纳米晶合金的结构、电磁性能及它们作为变压器铁芯使用的优点和缺点;论述了发展大块铁基纳米晶合金对于优化变压器性能的重要性以及配电变压器铁芯材料的发展趋势. 相似文献
14.
ＩＮＴＲＯＤＵＣＴＩＯＮＭｕｃｈａｔｔｅｎｔｉｏｎｈａｓｂｅｅｎｐａｉｄｒｅｃｅｎｔｌｙｔｏｔｈｅｓｔｕｄｙｏｆｓｐｉｎｐｏｌａｒｉｚｅｄｔｕｎｎｅｌｉｎｇｉｎｊｕｎｃｔｉｏｎｓｏｆｔｗｏｆｅｒｒｏｍａｇｎｅｔｓｓｅｐａｒａｔｅｄｂｙａｎｏｎｍａｇｎｅｔｉｃｔｕｎｎｅｌｉｎｇｂａｒｒｉｅｒ(Ｙａｏｉｅｔａｌ.,1993;Ｎｏｗａｋｅｔａｌ.,1992;Ｓｕｅｚａｗａｅｔａｌ.,1992;ＬｅＣｌａｉｒｅｔａｌ.,1994;Ｐｌａｓｋｅｔｔｅｔａｌ.,1994;Ｍｉｙａｚａｋｉｅｔａｌ.,1995;Ｔｅｚｕｋａｅｔａｌ.,1996).Ａｓｉｇｎｉ… 相似文献
15.
Manganese oxide La0.7Sr0.3MnO3 produced on (001) LaAlO3 substrate by means of sol-gel spincoating method was used as the base electrode of LaSrMnO/Al2O3/Fe tunnel junctions. The I-V characteristic in the high bias region of this system was shown to be similar to that of the
conventional tunnel junctions. Anomalous temperature dependence of tunneling resistance was observed to be a positive temperature
coefficient of resistance. This phenomenon was attributed to the high voltage applied and was simply elucidated from the density
states vs. energy diagram.
Project(199031) supported by the Science Foundation of Zhejiang Province. 相似文献
16.
FeCo基纳米晶合金具有良好的高频、高温磁性能,在航空航天领域有着广泛的应用前景,但其物理本质和微观机理尚不清楚。本文用原子力显微镜、高分辨场发射电子显微镜和透射电镜对FeCo纳米晶合金薄带横断面的介观结构进行了研究,发现退火温度和工作温度对其介观结构、介观尺寸上物质成份的迁移、滞留都有显著的影响,其结果决定着合金薄带的高温磁性能。 相似文献
17.
利用原子力显微镜和高分辨场发射电子显微镜系统地研究了高温退火的FeCo基纳米晶合金薄带的介观结构。发现高温退火的FeCo基纳米晶合金中具有纳米晶粒的团聚结构,尺寸约为200hm2由x射线衍射结果和目前已有的实验成果推断这种团聚结构中大约有104—105个纳米晶粒及包围这些纳米晶粒的非晶相。这种团聚结构与退火温度的高低具有十分密切的关系,因此称之为高温工作环境中FeCo基纳米晶合金的介观结构相,简称介观结构相。 相似文献
18.
Hui Xu Ph. D. Kai-yuan He Shu-li He Li-zhi Cheng Yuan-da Dong Xue-shan Xiao 《上海大学学报(英文版)》1999,3(4):318-320
１ Ｉｎｔｒｏｄｕｃｔｉｏｎ ＦｅｒｉｃｈｎａｎｏｃｒｙｓｔａｌｌｉｎｅＦｅＺｒＢａｌｌｏｙｓｓｉｍｕｌｔａｎｅｏｕｓｌｙｓｈｏｗｇｏｏｄｓｏｆｔｍａｇｎｅｔｉｃｐｒｏｐｅｒｔｉｅｓａｎｄｌａｒｇｅｓａｔｕｒａｔｉｏｎｍａｇｎｅｔｉｚａｔｉｏｎ［１,２］．Ｔｈｅｒｅａｒｅｍａｉｎｌｙｔｗｏｐｈａｓｅｓｉｎｔｈｅａｌｌｏｙｓｗｉｔｈｏｐｔｉｍｕｍｍａｇｎｅｔｉｃｐｒｏｐｅｒｔｉｅｓ：ａｎａｎｏｃｒｙｓｔａｌｌｉｎｅαＦｅｐｈａｓｅａｎｄａｎｉｎｔｅｒｇｒａｎｕｌａｒａｍｏｒｐｈｏｕｓｐｈａｓ… 相似文献
19.
A series of Li_(1-x)Na_xV_3O_8 materials was prepared by solution reaction followed by calcination method and their electrochemical performances in 2 M Li_2SO_4-water-ethanol solution as negative electrodes for aqueous electrolyte lithium ion battery were studied and compared each other.X-ray diffraction analysis revealed that partially substituting sodium for lithium in LiV_3O_8 could increase the interlayer distances of (100) plane.Cyclic voltammetric experiments have demonstrated that the Li~ insertion and extraction kinetics of Li_(0.7)Na_(0.3)V_3O_8 is superior to that of LiV_3O_8.Charge/discharge results showed that the discharge specific capacity of Li_(0.7)Na_(0.3)V_3O_8 electrode is higher than that of LiV_3O_8 electrode. 相似文献