GMAT备考精华：数学篇(二)
<p> 第二部分：数学基本概念</p><p> 1. <span word="mode">mode</span> 一堆数中出现频率最高的一个或几个数 <span word="e">e</span>.<span word="g">g</span>. <span word="mode">mode</span> <span word="of">of</span> 1,1,1,2,3,0,0,0,5 <span word="is">is</span> 1 <span word="and">and</span> 0</p><p> 2. <span word="range">range</span> 一堆数中最大和最小数之差 <span word="e">e</span>.<span word="g">g</span>. <span word="range">range</span> <span word="of">of</span> 1,1,2,3,5 <span word="is">is</span> 5-1=4</p><p> 3. <span word="mean">mean</span> <span word="arithmatic">arithmatic</span> <span word="mean">mean</span> <span word="geometric">geometric</span> <span word="mean">mean</span> <span word="n">n</span>个数之积的<span word="n">n</span>次方根</p><p> 4. <span word="median">median</span> 将一堆数排序之后，正中间的一个数， 或者中间两个数的平均数 <span word="e">e</span>.<span word="g">g</span>. <span word="median">median</span> <span word="of">of</span> 1,7,4,9,2,2,2,2,2,5,8 <span word="is">is</span> 2 <span word="median">median</span> <span word="of">of</span> 1,7,4,9,2,5 <span word="is">is</span> /2=6</p><p> 5. <span word="standard">standard</span> <span word="error">error</span> 一堆数中，每个数与平均数的差的绝对值之和，除以这堆数的个数 <span word="e">e</span>.<span word="g">g</span>. <span word="standard">standard</span> <span word="error">error</span> <span word="of">of</span> 0,2,5,7,6 <span word="is">is</span>: /5=2.4</p><p> 6. <span word="standard">standard</span> <span word="variation">variation</span> 一堆数中，每个数与平均数之差的平方之和，再除以<span word="n">n</span> <span word="e">e</span>.<span word="g">g</span>. <span word="standard">standard</span> <span word="variation">variation</span> <span word="of">of</span> 0,2,5,7,6 <span word="is">is</span>: _ 2 2 2 2 2_ |_ ++++_|/5=6.8</p><p> 7. <span word="standard">standard</span> <span word="deviation">deviation</span> 就是<span word="standard">standard</span> <span word="variation">variation</span>的平方根 标准方差的公式：<span word="d">d</span>^2=/<span word="n">n</span> <span word="d">d</span> 为标准方差</p><p> 8. 三角形 余玄定理<span word="C">C</span>^2=<span word="A">A</span>^2+<span word="B">B</span>^2-2<span word="ABCOSt">ABCOSt</span> <span word="t">t</span>为<span word="AB">AB</span>两条线间的夹角</p><p> 9. <span word="Y">Y</span>=<span word="k">k</span>1<span word="X">X</span>+<span word="B">B</span>1,<span word="Y">Y</span>=<span word="k">k</span>2<span word="X">X</span>+<span word="B">B</span>2，两线垂直的条件为<span word="K">K</span>1<span word="K">K</span>2=-1</p><p> 10.三的倍数的特点：所有位数之和可被3整除</p><p> 11. <span word="N">N</span>的阶乘公式: <span word="N">N</span>!=123....<span word="N">N</span> 且规定0!=1 例如 8!=12345678</p><p> 12. 熟悉一下根号2、3、5的值 <span word="sqrt">sqrt</span>=1.414 <span word="sqrt">sqrt</span>=1.732 <span word="sqrt">sqrt</span>=2.236 13. ...2/3 <span word="as">as</span> <span word="many">many</span> <span word="A">A</span> <span word="as">as</span> <span word="B">B</span>: <span word="A">A</span>=2/3<span word="B">B</span> ...<span word="twice">twice</span> <span word="as">as</span> <span word="many">many</span>... <span word="A">A</span> <span word="as">as</span> <span word="B">B</span>: <span word="A">A</span>=2<span word="B">B</span></p>
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