最新電大國(guó)際貿(mào)易原理期末考試小抄判斷題:1.世界貿(mào)易組織是一個(gè)非正式的國(guó)際組織 （錯(cuò)）2.按國(guó)際貿(mào)易內(nèi)容為依據(jù)，可劃分為出口貿(mào)易和進(jìn)口貿(mào)易（錯(cuò)）3.當(dāng)出口總值大于進(jìn)口總值時(shí)，成為貿(mào)易逆差 （錯(cuò)）4.國(guó)際貿(mào)易是人類發(fā)展到一定歷史階段的產(chǎn)物 （對(duì)）5.對(duì)外貿(mào)易值是以貨幣表示的對(duì)外貿(mào)易額 （對(duì)）1.貿(mào)易條件又稱貿(mào)易比價(jià) （對(duì)）2.世界最早的商品交易所施在比利時(shí)的安特衛(wèi)普建立的 （對(duì)）3.國(guó)富論的作者是李嘉圖 （錯(cuò)）4.世界市場(chǎng)價(jià)格是商品國(guó)際價(jià)值的貨幣表現(xiàn)，即以貨幣表現(xiàn)的商品的國(guó)際價(jià)值（對(duì)）5.亞當(dāng)斯密的國(guó)際貿(mào)易理論被稱為絕對(duì)利益理論 （對(duì)）6.商業(yè)機(jī)構(gòu)對(duì)商業(yè)機(jī)構(gòu)的電子商務(wù)為B2C （錯(cuò)）3.對(duì)一個(gè)國(guó)家來說，如果價(jià)格一直很高，進(jìn)口價(jià)格一直很低，則貿(mào)易條件會(huì)一直不利（錯(cuò)）3.國(guó)際分工是國(guó)際貿(mào)易的基礎(chǔ)（對(duì)）6.中國(guó)進(jìn)出口商品交易會(huì)又稱廣交會(huì)（對(duì)）1.凡期限在三年以上的投資成為長(zhǎng)期投資 （錯(cuò)）2.按資本特性，國(guó)際投資可分為對(duì)外直接投資和對(duì)外間接投資（對(duì)）3.瑞士的雀巢公司是跨國(guó)公司 （對(duì)）4.內(nèi)部化理論是有英國(guó)學(xué)者巴克利和卡森提出的 （對(duì)）5.建設(shè)-經(jīng)營(yíng)-移交簡(jiǎn)稱B-O-T （對(duì)）6.教育服務(wù)屬于服務(wù)貿(mào)易 （對(duì)）7.壟斷優(yōu)勢(shì)理論是金德爾伯創(chuàng)建的 （錯(cuò)）8.服務(wù)貿(mào)易組織總協(xié)定中的國(guó)民待遇適用于所有部門 （錯(cuò)）9.按資本來源，國(guó)際投資可分為公共投資和私人投資 （對(duì)）10.國(guó)際服務(wù)貿(mào)易中大多數(shù)服務(wù)具有無形性 (對(duì))1.全球配額屬于世界范圍的絕對(duì)配額 （對(duì)）2.進(jìn)口配額又稱出口限制額 （錯(cuò)）3.非關(guān)稅壁壘比關(guān)稅壁壘更具有隱蔽性和歧視性 （對(duì)）4.關(guān)稅是進(jìn)出口商品經(jīng)過已過一國(guó)關(guān)境時(shí)，由政府所設(shè)置的海關(guān)向其進(jìn)出口所征收的一種稅（對(duì)）5.普惠制的主要原則是普遍的、歧視的、非互惠的 （錯(cuò)）6.非關(guān)稅是指關(guān)稅以外限制進(jìn)口的各種措施 （對(duì)）7.名義關(guān)稅稅率越高，對(duì)本國(guó)同類產(chǎn)品的保護(hù)程度也越高 （對(duì)）8.對(duì)外貿(mào)易政策包括總政策和出口總政策 （對(duì)）9.雙邊貿(mào)易政策是由各國(guó)政府完全自主制定的外貿(mào)政策 （錯(cuò)）10.按照征稅待遇，關(guān)稅可分為普通關(guān)稅、優(yōu)惠關(guān)稅和進(jìn)口附加稅 （對(duì)）1.關(guān)稅與貿(mào)易總協(xié)定的原文分為序言和四大部分，共計(jì)36條（錯(cuò)）2.系統(tǒng)提出關(guān)稅同盟理論的是薩繆爾森 （錯(cuò)）3.自由貿(mào)易區(qū)不能免征關(guān)稅 （錯(cuò)）4.關(guān)稅同盟成立后可減少行政支出 （對(duì)）5.GATT的全稱是關(guān)稅與貿(mào)易總協(xié)定 （對(duì)）6.歐洲聯(lián)盟是當(dāng)今世界一體化程度最高的區(qū)域政治、經(jīng)濟(jì)集團(tuán) （對(duì)）7.保稅倉(cāng)庫(kù)是經(jīng)海關(guān)批準(zhǔn)專門用于存放保稅貨物的倉(cāng)庫(kù) （對(duì)）8.ITC的全稱是國(guó)際貿(mào)易委員會(huì) （對(duì)）6.外匯傾銷是出口企業(yè)利用本國(guó)貨幣對(duì)外貶值的機(jī)會(huì)，爭(zhēng)奪國(guó)外市場(chǎng)的特殊手段（對(duì)）2.關(guān)稅是一種直接稅（錯(cuò)）單選題:1.世界上主要的貿(mào)易大國(guó)不包括 （泰國(guó)）2.2010年中國(guó)貨物出口排名第幾 （1）3.一定時(shí)期內(nèi)的一國(guó)進(jìn)出口服務(wù)貿(mào)易中以百分比表示的各類項(xiàng)目的構(gòu)成稱為（對(duì)外服務(wù)貿(mào)易結(jié)構(gòu)）4.以下不屬于對(duì)外貿(mào)易依存度的形式是 （貿(mào)易條件）5.國(guó)際貿(mào)易按交易對(duì)象劃分不包括 （出口貿(mào)易）6.北美自由貿(mào)易區(qū)的成立時(shí)間 （1994）6.2010年5月24日，第二輪中美戰(zhàn)略與經(jīng)濟(jì)對(duì)話在（北京）舉行1.中國(guó)進(jìn)出口商品交易會(huì)于哪年創(chuàng)建 （1957）2.商業(yè)機(jī)構(gòu)對(duì)消費(fèi)者的電子商務(wù)為 （B2C）3.當(dāng)商品生產(chǎn)過剩時(shí)，商品價(jià)格 （趨跌）4.以下不屬于對(duì)銷貿(mào)易的是 （補(bǔ)償貿(mào)易）5.國(guó)富論的作者是 （亞當(dāng)斯密）6.以下不屬于固定組織形式的國(guó)際市場(chǎng)的是（加工貿(mào)易） 7.當(dāng)世界市場(chǎng)需求擴(kuò)大時(shí)，商品價(jià)格 （趨漲）1.以下不屬于借貸資本輸出的是 （證券投資）2.2010年，服務(wù)出口世界排名第一的是 （中國(guó)）3.世界上最大的直接投資東道國(guó)是 （美國(guó)）4.壟斷優(yōu)勢(shì)理論是誰(shuí)創(chuàng)建的 （海默）5.（）年4月15日，由111個(gè)國(guó)家和地區(qū)的代表正式簽署服務(wù)貿(mào)易總協(xié)定（1994） 6.獨(dú)資企業(yè)是指投入的資本完全由一國(guó)提供，外資股份占（95）以上的企業(yè) 7.國(guó)際生產(chǎn)折中理論 （鄧寧）1.以下不屬于非關(guān)稅壁壘的特點(diǎn) （公開性）2.以下不屬于技術(shù)貿(mào)易壁壘的特點(diǎn)是 （穩(wěn)定性）3.以進(jìn)口商品的價(jià)格為標(biāo)準(zhǔn)計(jì)征的關(guān)稅是 （從價(jià)稅）4.在總配額內(nèi)按國(guó)別或地區(qū)分配批給固定的配額，超過規(guī)定的配額便不準(zhǔn)進(jìn)口，這種配額方式是（國(guó)別配額） 5.反補(bǔ)貼稅又稱 （抵消稅）6.財(cái)政關(guān)稅又稱 （收入關(guān)稅）7.晚期重商主義學(xué)說的最重要代表人物是 （托馬斯.孟）7.以下不屬于按照征稅的商品流向分類的稅種是（優(yōu)惠關(guān)稅） 8.凱恩斯把反映投資增長(zhǎng)和國(guó)民收入擴(kuò)大之間的依存關(guān)系稱為 （投資乘數(shù)理論）1.共同市場(chǎng)理論的代表人物是 （西托夫斯基）2.以下哪個(gè)不屬于按時(shí)限長(zhǎng)短劃分的出口信貸種類 （買方信貸）3.我國(guó)在20世紀(jì)（）年代開始在沿海地區(qū)設(shè)立保稅區(qū) （90）4.WTO建立的時(shí)間是 （1995）5.2007年歐盟成員國(guó)的個(gè)數(shù) （27）6.（）年12月11日，中國(guó)正式成為世貿(mào)組織成員 （2001）多選題:1.當(dāng)代國(guó)際貿(mào)易包括 （ABCD 國(guó)際貨物貿(mào)易；國(guó)際服務(wù)貿(mào)易；國(guó)際技術(shù)貿(mào)易；國(guó)際投資）2.國(guó)際貿(mào)易按貨物移動(dòng)方向劃分為 （ABCDE 出口貿(mào)易；進(jìn)口貿(mào)易；過境貿(mào)易；復(fù)出口與復(fù)進(jìn)口；凈出口與凈進(jìn)口）3.國(guó)際貿(mào)易按交易內(nèi)容可劃分為 （ABC 國(guó)際貨物貿(mào)易；國(guó)際服務(wù)貿(mào)易；國(guó)際技術(shù)貿(mào)易）4.國(guó)際服務(wù)貿(mào)易的提供方式 （ABD 跨境提供；境外消費(fèi)；自然人流動(dòng)）1.貿(mào)易條件變化的影響因素有 （ABCD 選擇的年份不同；出口價(jià)格；進(jìn)口價(jià)格；出口數(shù)量指數(shù)）2.招標(biāo)投標(biāo)業(yè)務(wù)包括的步驟 （ABCD 招標(biāo)；投標(biāo)；開標(biāo)；簽約 ）3.對(duì)里昂惕夫反論的解釋及有關(guān)學(xué)說有 （ABCD勞動(dòng)熟練說；人力資本本說；技術(shù)差距說；產(chǎn)品周期說）4.貿(mào)易條件的種類有 （ABCD 凈貿(mào)易條件按；收入貿(mào)易條件；單項(xiàng)因素貿(mào)易條件；雙項(xiàng)因素條件）5.當(dāng)代國(guó)際分工的特點(diǎn)是 （ABCD發(fā)達(dá)國(guó)家居國(guó)際分工的主導(dǎo)地位；國(guó)際分工類型多樣化；發(fā)達(dá)國(guó)家與發(fā)展中國(guó)家間工業(yè)分工的形式發(fā)生變化；區(qū)域性經(jīng)貿(mào)集團(tuán)內(nèi)部分工加強(qiáng)）6.代理可分為 （BCD 包銷；獨(dú)家代理；一般代理）7.拍賣的出價(jià)方法 （BCD 增價(jià)拍賣；減價(jià)拍賣；密封遞價(jià)拍賣）1.中國(guó)服務(wù)貿(mào)易發(fā)展特點(diǎn) （ABCD服務(wù)貿(mào)易增速高于全球水平；服務(wù)貿(mào)易長(zhǎng)期逆差；服務(wù)外包產(chǎn)業(yè)迅速發(fā)展；服務(wù)貿(mào)易區(qū)域發(fā)展極不平衡）2.國(guó)際技術(shù)貿(mào)易的方法有 （ABCD 直接投資；許可貿(mào)易；咨詢服務(wù)和技術(shù)服務(wù)；合作生產(chǎn)）3.以下屬于服務(wù)貿(mào)易的是 （ABCD 通信服務(wù)；金融服務(wù)；銷售服務(wù)；教育服務(wù)）4.以下屬于跨國(guó)公司的是 （ABCD愛迪生電氣公司；龍尼萊佛公司；瑞士的雀巢公司；帝國(guó)化學(xué)公司）5.第二次世界大戰(zhàn)后國(guó)際投資的特點(diǎn)是 （ABCD國(guó)際直接投資占主導(dǎo)地位 ；國(guó)際投資中的主體仍是西方發(fā)達(dá)國(guó)家；國(guó)際資本移動(dòng)的流向發(fā)生了重大變化；對(duì)外直接投資的部門結(jié)構(gòu)發(fā)生了顯著變化）6.跨國(guó)公司運(yùn)用轉(zhuǎn)移價(jià)格的主要目的有 （ABCD 減少稅負(fù)；轉(zhuǎn)移資金；調(diào)節(jié)利潤(rùn)水平；增強(qiáng)子公司在國(guó)際市場(chǎng)的上競(jìng)爭(zhēng)能力）7.借貸資本輸出的方式有 （ABCD 政府援助貸款；借貸資本輸出的方式；國(guó)際金融市場(chǎng)貸款；出口信貸）1.技術(shù)性貿(mào)易壁壘的主要內(nèi)容有 （ABCD 技術(shù)標(biāo)準(zhǔn)；技術(shù)法規(guī)；合格評(píng)定程序；綠色貿(mào)易壁壘）2.外匯管制一般包括 （BCD數(shù)量性外匯管制；成本性外匯管制；混合型外匯管制）3.海關(guān)稅則的主要種類有 （ABCD 單式稅則；復(fù)式稅則；自主稅則；協(xié)定稅則）4.晚期重商主義學(xué)說的政策與措施 （ABCD禁止若干國(guó)外商品；課征保護(hù)關(guān)稅；出口退稅；保護(hù)農(nóng)業(yè)）5.關(guān)稅稅率表主要包括三個(gè)部分，分別是 （BCD 稅則號(hào)列；貨物分類目錄；稅率）6.按照商品流向分類，可分為 （ACD 進(jìn)口稅；出口稅；過境稅）7.綠色貿(mào)易壁壘主要有以下幾種形式 （BCD環(huán)境技術(shù)法規(guī)與標(biāo)準(zhǔn)；產(chǎn)品檢疫制度；綠色標(biāo)志）8.對(duì)外貿(mào)易政策的層次 （ABCD單邊貿(mào)易政策；雙邊貿(mào)易政策；諸邊貿(mào)易政策；多變貿(mào)易政策）1.世貿(mào)組織的基本原則 （ABCD非歧視原則；市場(chǎng)開放原則；公平競(jìng)爭(zhēng)原則；透明度原則）2.區(qū)域經(jīng)濟(jì)一體化按貿(mào)易壁壘取消的程度可劃分為 （ABCDE優(yōu)惠貿(mào)易安排；自由貿(mào)易區(qū)；關(guān)稅同盟；共同市場(chǎng)；經(jīng)濟(jì)聯(lián)盟）3.出口信貸按時(shí)間可分為 （ABC短期信貸；中期信貸，長(zhǎng)期信貸）4.以下屬于世貿(mào)組織機(jī)構(gòu)的是 （ABCDE部長(zhǎng)會(huì)議；總理事會(huì)；理事會(huì)；委員會(huì)；秘書處）5.商品傾銷的種類可分為 （ABC偶然性傾銷；間歇性傾銷；長(zhǎng)期性傾銷）6.關(guān)稅同盟的動(dòng)態(tài)效果有 （ABCD 資源合理配置；獲取規(guī)模經(jīng)濟(jì)利益；刺激投資；加速經(jīng)濟(jì)發(fā)展）3.世貿(mào)組織協(xié)議的主要內(nèi)容 （ABCDE世貿(mào)組織的宗旨；世貿(mào)組織的范圍、職能；世貿(mào)組織的機(jī)構(gòu)與法律地位；世貿(mào)組織的成員；世貿(mào)組織的決策方式）請(qǐng)您刪除一下內(nèi)容，O(_)O謝謝！2016年中央電大期末復(fù)習(xí)考試小抄大全，電大期末考試必備小抄，電大考試必過小抄Acetylcholine is a neurotransmitter released from nerve endings (terminals) in both the peripheral and the central nervous systems. It is synthesized within the nerve terminal from choline, taken up from the tissue fluid into the nerve ending by a specialized transport mechanism. The enzyme necessary for this synthesis is formed in the nerve cell body and passes down the axon to its end, carried in the axoplasmic flow, the slow movement of intracellular substance (cytoplasm). Acetylcholine is stored in the nerve terminal, sequestered in small vesicles awaiting release. When a nerve action potential reaches and invades the nerve terminal, a shower of acetylcholine vesicles is released into the junction (synapse) between the nerve terminal and the effector cell which the nerve activates. This may be another nerve cell or a muscle or gland cell. Thus electrical signals are converted to chemical signals, allowing messages to be passed between nerve cells or between nerve cells and non-nerve cells. This process is termed chemical neurotransmission and was first demonstrated, for nerves to the heart, by the German pharmacologist Loewi in 1921. Chemical transmission involving acetylcholine is known as cholinergic. Acetylcholine acts as a transmitter between motor nerves and the fibres of skeletal muscle at all neuromuscular junctions. At this type of synapse, the nerve terminal is closely apposed to the cell membrane of a muscle fibre at the so-called motor end plate. On release, acetylcholine acts almost instantly, to cause a sequence of chemical and physical events (starting with depolarization of the motor endplate) which cause contraction of the muscle fibre. This is exactly what is required for voluntary muscles in which a rapid response to a command is required. The action of acetylcholine is terminated rapidly, in around 10 milliseconds; an enzyme (cholinesterase) breaks the transmitter down into choline and an acetate ion. The choline is then available for re-uptake into the nerve terminal. These same principles apply to cholinergic transmission at sites other than neuromuscular junctions, although the structure of the synapses differs. In the autonomic nervous system these include nerve-to-nerve synapses at the relay stations (ganglia) in both the sympathetic and the parasympathetic divisions, and the endings of parasympathetic nerve fibres on non-voluntary (smooth) muscle, the heart, and glandular cells; in response to activation of this nerve supply, smooth muscle contracts (notably in the gut), the frequency of heart beat is slowed, and glands secrete. Acetylcholine is also an important transmitter at many sites in the brain at nerve-to-nerve synapses. To understand how acetylcholine brings about a variety of effects in different cells it is necessary to understand membrane receptors. In post-synaptic membranes (those of the cells on which the nerve fibres terminate) there are many different sorts of receptors and some are receptors for acetylcholine. These are protein molecules that react specifically with acetylcholine in a reversible fashion. It is the complex of receptor combined with acetylcholine which brings about a biophysical reaction, resulting in the response from the receptive cell. Two major types of acetylcholine receptors exist in the membranes of cells. The type in skeletal muscle is known as nicotinic; in glands, smooth muscle, and the heart they are muscarinic; and there are some of each type in the brain. These terms are used because nicotine mimics the action of acetylcholine at nicotinic receptors, whereas muscarine, an alkaloid from the mushroom Amanita muscaria, mimics the action of acetylcholine at the muscarinic receptors. Acetylcholine is the neurotransmitter produced by neurons referred to as cholinergic neurons. In the peripheral nervous system acetylcholine plays a role in skeletal muscle movement, as well as in the regulation of smooth muscle and cardiac muscle. In the central nervous system acetylcholine is believed to be involved in learning, memory, and mood. Acetylcholine is synthesized from choline and acetyl coenzyme A through the action of the enzyme choline acetyltransferase and becomes packaged into membrane-boundvesicles. After the arrival of a nerve signal at the termination of an axon, the vesicles fuse with the cell membrane, causing the release of acetylcholine into thesynaptic cleft. For the nerve signal to continue, acetylcholine must diffuse to another nearby neuron or muscle cell, where it will bind and activate areceptorprotein. There are two main types of cholinergic receptors, nicotinic and muscarinic. Nicotinic receptors are located at synapses between two neurons and at synapses between neurons and skeletal muscle cells. Upon activation a nicotinic receptor acts as a channel for the movement of ions into and out of the neuron, directly resulting indepolarizationof the neuron. Muscarinic receptors, located at the synapses of nerves with smooth or cardiac muscle, trigger a chain of chemical events referred to as signal transduction. For a cholinergic neuron to receive another impulse, acetylcholine must be released from the receptor to which it has bound. This will only happen if the concentration of acetylcholine in the synaptic cleft is very low. Low synaptic concentrations of acetylcholine can be maintained via a hydrolysis reaction catalyzed by the enzyme acetylcholinesterase. This enzyme hydrolyzes acetylcholine into acetic acid and choline. If acetylcholinesterase activity is inhibited, the synaptic concentration of acetylcholine will remain higher than normal. If this inhibition is irreversible, as in the case of exposure to many nerve gases and some pesticides, sweating, bronchial constriction, convulsions, paralysis, and possibly death can occur. Although irreversible inhibition is dangerous, beneficial effects may be derived from transient (reversible) inhibition. Drugs that inhibit acetylcholinesterase in a reversible manner have been shown to improve memory in some people with Alzheimers disease. abstract expressionism, movement of abstract painting that emerged in New York City during the mid-1940s and attained singular prominence in American art in the following decade; also called action painting and the New York school. It was the first important school in American painting to declare its independence from European styles and to influence the development of art abroad. Arshile Gorky first gave impetus to the movement. His paintings, derived at first from the art of Picasso, Mir, and surrealism, became more personally expressive. Jackson Pollocks turbulent yet elegant abstract paintings, which were created by spattering paint on huge canvases placed on the floor, brought abstract expressionism before a hostile public. Willem de Koonings first one-man show in 1948 established him as a highly influential artist. His intensely complicated abstract paintings of the 1940s were followed by images of Woman, grotesque versions of buxom womanhood, which were virtually unparalleled in the sustained savagery of their execution. Painters such as Philip Guston and Franz Kline turned to the abstract late in the 1940s and soon developed strikingly original stylesthe former, lyrical and evocative, the latter, forceful and boldly dramatic. Other important artists involved with the movement included Hans Hofmann, Robert Motherwell, and Mark Rothko; among other major abstract expressionists were such painters as Clyfford Still, Theodoros Stamos, Adolph Gottlieb, Helen Frankenthaler, Lee Krasner, and Esteban Vicente. Abstract expressionism presented a broad range of stylistic diversity within its largely, though not exclusively, nonrepresentational framework. For example, the expressive violence and activity in paintings by de Kooning or Pollock marked the opposite end of the pole from the simple, quiescent images of Mark Rothko. Basic to most abstract expressionist painting were the attention paid to surface qualities, i.e., qualities of brushstroke and texture; the use of huge canvases; the adoption of an approach to space in which all parts of the canvas played an equally vital role in the total work; the harnessing of accidents that occurred during the process of painting; the glorification of the act of painting itself as a means of visual communication; and the attempt to transfer pure emotion directly onto the canvas. The movement had an inestimable influence on the many varieties of work that followed it, especially in the way its proponents used color and materials. Its essential energy transmitted an enduring excitement to the American art scene. Science and technology is quite a broad category, and it covers everything from studying the stars and the planets to studying molecules and viruses. Beginning with the Greeks and Hipparchus, continuing through Ptolemy, Copernicus and Galileo, and today with our work on the International Space Station, man continues to learn more and more about the heavens. From here, we look inward to biochemistry and biology. To truly understand biochemistry, scientists study and see the unseen bystudying the chemistry of biological processes. This science, along with biophysics, aims to bring a better understanding of how bodies work from how we turn food into energy to how nerve impulses transmit.analytic geometry, branch ofgeometryin which points are represented with respect to a coordinate system, such asCartesian coordinates, and in which the approach to geometric problems is primarily algebraic. Its most common application is in the representation of equations involving two or three variables as curves in two or three dimensions or surfaces in three dimensions. For example, the linear equationax+by+c=0 represents a straight line in thexy-plane, and the linear equationax+by+cz+d=0 represents a plane in space, wherea, b, c,anddare constant numbers (coefficients). In this way a geometric problem can be translated into an algebraic problem and the methods of algebra brought to bear on its solution. Conversely, the solution of a problem in algebra, such as finding the roots of an equation or system of equations, can be estimated or sometimes given exactly by geometric means, e.g., plotting curves and surfaces and determining points of intersection. In plane analytic geometry a line is frequently described in terms of its slope, which expresses its inclination to the coordinate axes; technically, the slopemof a straight line is the (trigonometric) tangent of the angle it makes with thex-axis. If the line is parallel to thex-axis, its slope is zero. Two or more lines with equal slopes are parallel to one another. In general, the slope of the line through the points (x1,y1) and (x2,y2) is given bym= (y2-y1) / (x2-x1). The conic sections are treated in analytic geometry as the curves corresponding to the general quadratic equationax2+bxy+cy2+dx+ey+f=0, wherea, b, fare constants anda, b,andcare not all zero. In solid analytic geometry the orientation of a straight line is given not by one slope but by its direction cosines, , , and , the cosines of the angles the line makes with thex-, y-,andz-axes, respectively; these satisfy the relationship 2+2+2= 1. In the same way that the conic sections are studied in two dimensions, the 17 quadric surfaces, e.g., the ellipsoid, paraboloid, and elliptic paraboloid, are studied in solid analytic geometry in terms of the general equationax2+by2+cz2+dxy+exz+fyz+px+qy+rz+s=0. The methods of analytic geometry have been generalized to four or more dimensions and have been combined with other branches of geometry. Analytic geometry was introduced by RenDescartesin 1637 and was of fundamental importance in the development of thecalculusby Sir Isaac Newton and G. W. Leibniz in the late 17th cent. More recently it has served as the basis for the modern development and exploitation ofalgebraic geometry. circle, closed plane curve consisting of all points at a given distance from some fixed point, called the center. A circle is a conic section cut by a plane perpendicular to the axis of the cone. The term circle is also used to refer to the region enclosed by the curve, more properly called a circular region. The radius of a circle is any line segment connecting the center and a point on the curve; the term is also used for the length r of this segment, i.e., the common distance of all points on the curve from the center. Similarly, the circumference of a circle is either the curve itself or its length of arc. A line segment whose two ends lie on the circumference is a chord; a chord through the center is the diameter. A secant is a line of indefinite length intersecting the circle at two points, the segment of it within the circle being a chord. A tangent to a circle is a straight line touching the circle at only one point, the point of contact, or tangency, and is always perpendicular to the radius drawn to this point. A circle is inscribed in a polygon if each side of the polygon is tangent to the circle; a circle is circumscribed about a polygon if all the vertices of the polygon lie on the circumference. The length of the circumference C of a circle is equal to (see pi) times twice the radius distance r, or C=2r. The area A bounded by a circle is given by A=r2. Greek geometry left many unsolved problems about circles, including the problem of squaring the circle, i.e., constructing a square with an area equal to that of a given circle, using only a straight edge and compass; it was finally proved impossible in the late 19th cent. (see geometric problems of antiquity). In modern mathematics the circle is the basis for such theories as inversive geometry and certain non-Euclidean geometries. The circle figures significantly in many cultures. In religion and art it frequently symbolizes heaven, eternity, or the universe.