费费数学宝典(连载十九)
<p> 以下为大家连载<span word="GMAT">GMAT</span>数学考试备考宝书，费费数学宝典，希望大家备考顺利，成绩高高，都能申请到理想的美国大学!</p><p> 41、<span word="X">X</span>是否满足：0</p><p> (1)<span word="X">X</span>^23次根号<span word="X">X</span>;</p><p> (2)<span word="X">X</span>^33次根号<span word="X">X</span>;</p><p> 【答案】<span word="A">A</span></p><p> 【思路】</p><p> 看(1)，<span word="x">x</span>一定大于0，所以0</p><p> 看(2)，0</p><p> 42、<span word="S">S</span>是一个数列(<span word="A">A</span>1,<span word="A">A</span>2,,<span word="An">An</span>)，可否求出数列的标准方差?</p><p> (1)每个数相等;</p><p> (2)数列的算术平均数是7;</p><p> 【答案】<span word="A">A</span></p><p> 【思路】每个数相等,那么标准方差为0</p><p> 只知道数列的算术平均数,不知各数的离散程序,无法求出标准方差.</p><p> 43、<span word="TU">TU</span>是个两位数(<span word="T">T</span>是十位数，<span word="U">U</span>是个位数)。<span word="TU">TU</span> <span word="is">is</span> <span word="twice">twice</span> <span word="product">product</span> <span word="of">of</span> <span word="these">these</span> <span word="digits">digits</span>, <span word="U">U</span>=?</p><p> 【答案】6</p><p> 【思路】由题意，10<span word="T">T</span>+<span word="U">U</span>=2<span word="TU">TU</span>--</p><p> <span word="U">U</span>=10<span word="T">T</span>/</p><p> <span word="U">U</span>=10<span word="T">T</span>-5+5/</p><p> <span word="U">U</span>=5+)</p><p> 又，由<span word="U">U</span>,<span word="T">T</span>的定义域可得<span word="T">T</span>=3,<span word="U">U</span>=6。</p><p> </p>
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