新GRE数学末重要考点指导
<p> 针对新版<span word="gre">gre</span>数学复习，将每天为大家整理一个重要考点，希望大家能够将这些重要考点系统地记住，在考试中取得一个好成绩，突破新<span word="gre">gre</span>数学困境。</p><p> 新版<span word="gre">gre</span>数学复习重要考点：<span word="Sum">Sum</span> <span word="of">of</span> <span word="Arithmetic">Arithmetic</span> <span word="Progression">Progression</span>（数列求和）</p><p> <span word="The">The</span> <span word="sum">sum</span> <span word="of">of</span> <span word="n">n</span>-<span word="numbers">numbers</span> <span word="of">of</span> <span word="an">an</span> <span word="arithmetic">arithmetic</span> <span word="progression">progression</span> <span word="is">is</span> <span word="given">given</span> <span word="by">by</span></p><p> <span word="S">S</span>=<span word="nxdn">nxdn</span>（<span word="n">n</span>-1）/2</p><p> <span word="where">where</span> <span word="x">x</span> <span word="is">is</span> <span word="the">the</span> <span word="first">first</span> <span word="number">number</span> <span word="and">and</span> <span word="d">d</span> <span word="is">is</span> <span word="the">the</span> <span word="constant">constant</span> <span word="increment">increment</span>.</p><p> <span word="example">example</span>：</p><p> <span word="sum">sum</span> <span word="of">of</span> <span word="first">first</span> 10 <span word="positive">positive</span> <span word="odd">odd</span> <span word="numbers">numbers</span>:101+2109/2=10+90=100</p><p> <span word="sum">sum</span> <span word="of">of</span> <span word="first">first</span> 10 <span word="multiples">multiples</span> <span word="of">of</span> 7 <span word="starting">starting</span> <span word="at">at</span> 7： 107+7109/2=70+315=385</p><p> <span word="remember">remember</span>：</p><p> <span word="For">For</span> <span word="a">a</span> <span word="descending">descending</span> <span word="AP">AP</span> <span word="the">the</span> <span word="constant">constant</span> <span word="difference">difference</span> <span word="is">is</span> <span word="negative">negative</span>.</p><p> 由于美国数学基础教育的难度增加导致数学考试越来越难，但新<span word="gre">gre</span>数学复习考点都是高中时候学到的知识点，考生不要过于紧张，把基本概念弄明白，再记住一些新版<span word="gre">gre</span>数学必备的词汇，那么相信新版<span word="gre">gre</span>数学应该没有问题。</p><p> <span word="AP">AP</span></p><p> <span word="Average">Average</span> <span word="of">of</span> <span word="n">n</span> <span word="numbers">numbers</span> <span word="of">of</span> <span word="arithmetic">arithmetic</span> <span word="progression">progression</span> （<span word="AP">AP</span>） <span word="is">is</span> <span word="the">the</span> <span word="average">average</span> <span word="of">of</span> <span word="the">the</span> <span word="smallest">smallest</span> <span word="and">and</span> <span word="the">the</span> <span word="largest">largest</span> <span word="number">number</span> <span word="of">of</span> <span word="them">them</span>. <span word="The">The</span> <span word="average">average</span> <span word="of">of</span> <span word="m">m</span> <span word="number">number</span> <span word="can">can</span> <span word="also">also</span> <span word="be">be</span> <span word="written">written</span> <span word="as">as</span> <span word="x">x</span> + <span word="d">d</span>（<span word="m">m</span>-1）/2.</p><p> <span word="Example">Example</span>：</p><p> <span word="The">The</span> <span word="average">average</span> <span word="of">of</span> <span word="all">all</span> <span word="integers">integers</span> <span word="from">from</span> 1 <span word="to">to</span> 5 <span word="is">is</span> （1+5）/2=3</p>
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