第290章 书海

　　四、圆的方程：
　　1、圆的标准方程：在平面直角坐标系中，以点O（a，b）为圆心，以r为半径的圆的标准方程是（x-a）^2+（y-b）^2=r^2。
　　2、圆的一般方程：把圆的标准方程展开，移项，合并同类项后，可得圆的一般方程是x^2+y^2+Dx+Ey+F=0。和标准方程对比，其实D=-2a，E=-2b，F=a^2+b^2。
　　五、圆和点的位置关系：
　　以点P与圆O的为例（设P是一点,则PO是点到圆心的距离）,P在⊙O外,PO＞r；P在⊙O上,PO＝r；P在⊙O内,PO＜r.
　　六、直线与圆有3种位置关系：
　　无公共点为相离；
　　有两个公共点为相交；
　　圆与直线有唯一公共点为相切。这条直线叫做圆的切线,这个唯一的公共点叫做切点.以直线AB与圆O为例（设OP⊥AB于P,则PO是AB到圆心的距离）：AB与⊙O相离,PO＞r；AB与⊙O相切,PO＝r；AB与⊙O相交,PO＜r。
　　一、圆的性质
　　（1）圆是轴对称图形，其对称轴是任意一条通过圆心的直线。圆也是中心对称图形，其对称中心是圆心。
　　垂径定理：垂直于弦的直径平分这条弦，并且平分弦所对的2条弧。
　　垂径定理的逆定理：平分弦（不是直径）的直径垂直于弦，并且平分弦所对的2条弧。
　　（2）有关圆周角和圆心角的性质和定理
　　①在同圆或等圆中，如果两个圆心角，两个圆周角，两组弧，两条弦，两条弦心距中有一组量相等，那么他们所对应的其余各组量都分别相等。
　　②在同圆或等圆中，相等的弧所对的圆周角等于它所对的圆心角的一半（圆周角与圆心角在弦的同侧）。
　　直径所对的圆周角是直角。90度的圆周角所对的弦是直径。
　　圆心角计算公式：θ=(L/2πr)×360°=180°L/πr=L/r(弧度)。
　　即圆心角的度数等于它所对的弧的度数；圆周角的度数等于它所对的弧的度数的一半。
　　③如果一条弧的长是另一条弧的2倍，那么其所对的圆周角和圆心角是另一条弧的2倍。
　　（3）有关外接圆和内切圆的性质和定理
　　①一个三角形有唯一确定的外接圆和内切圆。外接圆圆心是三角形各边垂直平分线的交点，到三角形三个顶点距离相等；
　　②内切圆的圆心是三角形各内角平分线的交点，到三角形三边距离相等。
　　③R=2S△÷L（R：内切圆半径，S：三角形面积，L：三角形周长）。
　　④两相切圆的连心线过切点。（连心线：两个圆心相连的直线）
　　⑤圆O中的弦PQ的中点M，过点M任作两弦AB，CD，弦AC与BD分别交PQ于X，Y，则M为XY之中点。
　　（4）如果两圆相交，那么连接两圆圆心的线段（直线也可）垂直平分公共弦。
　　（5）弦切角的度数等于它所夹的弧的度数的一半。
　　（6）圆内角的度数等于这个角所对的弧的度数之和的一半。
　　（7）圆外角的度数等于这个角所截两段弧的度数之差的一半。
　　（8）周长相等，圆面积比正方形、长方形、三角形的面积大。
　　不仅仅有这些文字，还有大大的配图，柳素月感觉到非常的详细，但是他实在是一些看不懂这些是什么东西，但是起码定理来说，能理解一半，看起来也并不是全部都不知道。
　　看来这个东西非常的管用，什么资料他都能搜到。
　　“是不是不光能搜到你这些奇怪的东西？还能搜到点儿正儿八经的书籍？”柳素月幽幽地问道。
　　金英笑着说道：“奇怪，有什么可奇怪的，这些都是正儿八经的知识呢，不过你想搜一搜你们古代的书籍，这里面也是有的。我告诉你，这里面什么都可能有，就连外面的东西也有，你可以搜一搜。”
　　“好，我先搜一搜我们这里的书，然后再搜一搜外面的书。”柳素月点了点头。
　　“搜一搜滕王阁序！”柳素月大声地吼道。
　　立即一本古书就出现了，蓝色的封皮，用绳子固定的侧面，泛淡黄的宣纸，迅速地就翻开了那页：
　　《滕王阁序》
　　豫章故郡，洪都新府。星分翼轸，地接衡庐。襟三江而带五湖，控蛮荆而引瓯越。物华天宝，龙光射牛斗之墟；人杰地灵，徐孺下陈蕃之榻。雄州雾列，俊采星驰。台隍枕夷夏之交，宾主尽东南之美。都督阎公之雅望，棨戟遥临；宇文新州之懿范，襜帷暂驻。十旬休假，胜友如云；千里逢迎，高朋满座。腾蛟起凤，孟学士之词宗；紫电青霜，王将军之武库。家君作宰，路出名区；童子何知，躬逢胜饯。时维九月，序属三秋。潦水尽而寒潭清，烟光凝而暮山紫。俨骖騑于上路，访风景于崇阿；临帝子之长洲，得天人之旧馆。层峦耸翠，上出重霄；飞阁流丹，下临无地。鹤汀凫渚，穷岛屿之萦回；桂殿兰宫，即冈峦之体势。披绣闼，俯雕甍，山原旷其盈视，川泽纡其骇瞩。闾阎扑地，钟鸣鼎食之家；舸舰弥津，青雀黄龙之舳。云销雨霁，彩彻区明。落霞与孤鹜齐飞，秋水共长天一色。渔舟唱晚，响穷彭蠡之滨；雁阵惊寒，声断衡阳之浦。遥襟甫畅，逸兴遄飞。爽籁发而清风生，纤歌凝而白云遏。睢园绿竹，气凌彭泽之樽；邺水朱华，光照临川之笔。四美具，二难并。穷睇眄于中天，极娱游于暇日。天高地迥，觉宇宙之无穷；兴尽悲来，识盈虚之有数。望长安于日下，目吴会于云间。地势极而南溟深，天柱高而北辰远。关山难越，谁悲失路之人？萍水相逢，尽是他乡之客。怀帝阍而不见，奉宣室以何年？嗟乎！时运不齐，命途多舛。冯唐易老，李广难封。屈贾谊于长沙，非无圣主；窜梁鸿于海曲，岂乏明时？所赖君子见机，达人知命。老当益壮，宁移白首之心？穷且益坚，不坠青云之志。酌贪泉而觉爽，处涸辙以犹欢。北海虽赊，扶摇可接；东隅已逝，桑榆非晚。孟尝高洁，空余报国之情；阮籍猖狂，岂效穷途之哭！勃，三尺微命，一介书生。无路请缨，等终军之弱冠；有怀投笔，慕宗悫之长风。舍簪笏于百龄，奉晨昏于万里。非谢家之宝树，接孟氏之芳邻。他日趋庭，叨陪鲤对；今兹捧袂，喜托龙门。杨意不逢，抚凌云而自惜；钟期既遇，奏流水以何惭？呜乎！胜地不常，盛筵难再；兰亭已矣，梓泽丘墟。临别赠言，幸承恩于伟饯；登高作赋，是所望于群公。敢竭鄙怀，恭疏短引；一言均赋，四韵俱成。请洒潘江，各倾陆海云尔：滕王高阁临江渚，佩玉鸣鸾罢歌舞。画栋朝飞南浦云，珠帘暮卷西山雨。闲云潭影日悠悠，物换星移几度秋。阁中帝子今何在？槛外长江空自流。
　　柳素月叹息着说道：“看来还真有。”
　　“你不信再搜一搜外国书籍，绝对有的。”金英道。
　　“我不知道什么书籍，你给我提供几个吧！”柳素月道。
　　“没问题啊！你可以搜一搜《简爱》，是一本很不错的小说。”金英道。
　　“好得，我现在都做尝试。”柳素月点了点头。
　　“搜一搜《简爱》！”柳素月大声的喊道。
　　一本牛皮纸包裹的书皮出现了，封面画着漂亮的图案，不过看起来就像是西方油画，大大的写着中英文的《简爱》两个大字。
　　柳素月打开了一段阅读了文字。
　　THERE was no possibility of taking a walk that day.We had been wandering, indeed, in theleafless shrubbery an hour in the morning; but since dinner (Mrs.Reed,when there was nocompany,dined early) the cold winter wind had brought with it clouds so sombre, and a rain sopenetrating, that further outdoor exercise was now out of the question. I was glad of it: I neverliked long walks, especially on chilly afternoons:dreadful to me was the coming home in the rawtwilight,with nipped fingers and toes, and a heart saddened by the chidings of Bessie, the nurse,and humbled by the consciousness of my physical inferiority to Eliza,John,and Georgiana Reed.The said Eliza, John, and Georgiana were now clustered round their mama in the drawing-room:she lay reclined on a sofa by the fireside, and with her darlings about her (for the time neitherquarrelling nor crying) looked perfectly happy.Me, she had dispensed from j oining the group;saying, 'She regretted to be under the necessity of keeping me at a distance;but that until sheheard from Bessie, and could discover by her own observation, that I was endeavouring in goodearnest to acquire a more sociable and childlike disposition, a more attractive and sprightlymanner- something lighter, franker,more natural, as it were- she really must exclude me fromprivileges intended only for contented,happy, little children.''What does Bessie say I have done?' I asked.
'Jane, I don't like cavillers or questioners;besides, there is something truly forbidding in a childtaking up her elders in that manner.Be seated somewhere; and until you can speak pleasantly,remain silent.'
A small breakfast-room adjoined the drawing-room, I slipped in there. It contained a bookcase: Isoon possessed myself of a volume, taking care that it should be one stored with pictures. Imounted into the window-seat:gathering up my feet, I sat cross-legged, like a Turk; and,havingdrawn the red moreen curtain nearly close, I was shrined in double retirement.Folds of scarletdrapery shut in my view to the right hand; to the left were the clear panes of glass,protecting,butnot separating me from the drear November day.At intervals,while turning over the leaves of mybook, I studied the aspect of that winter afternoon.Afar, it offered a pale blank of mist and cloud;near a scene of wet lawn and storm-beat shrub,with ceaseless rain sweeping away wildly before along and lamentable blast. I returned to my book-Bewick's History of British Birds: the letterpressthereof I cared little for, generally speaking; and yet there were certain introductory pages that,child as I was, I could not pass quite as a blank.They were those which treat of the haunts ofsea-fowl;of'the solitary rocks and promontories'by them only inhabited;of the coast of Norway,studded with isles from its southern extremity, the Lindeness,or Naze, to the North Cape- 'Wherethe Northern Ocean, in vast whirls,Boils round the naked,melancholy isles Of farthest Thule;and the Atlantic surge Pours in among the stormy Hebrides.'Nor could I pass unnoticed thesuggestion of the bleak shores of Lapland,Siberia,Spitzbergen,Nova Zembla, Iceland,Greenland,with'the vast sweep of the Arctic Zone, and those forlorn regions of dreary space,- that reservoirof frost and snow,where firm fields of ice, the accumulation of centuries of winters, glazed inAlpine heights above heights, surround the pole and concentre the multiplied rigours of extremecold.' Of these death-white realms I formed an idea of my own: shadowy, like all thehalf-comprehended notions that float dim through children's brains,but strangely impressive.Thewords in these introductory pages connected themselves with the succeeding vignettes, and gavesignificance to the rock standing up alone in a sea of billow and spray; to the broken boat strandedon a desolate coast; to the cold and ghastly moon glancing through bars of cloud at a wreck justsinking.