GMAT数学备考资料：费费数学宝典详解版(十)
<p> 11、<span word="S">S</span>=，<span word="T">T</span>=。<span word="One">One</span> <span word="number">number</span> <span word="is">is</span> <span word="selected">selected</span> <span word="from">from</span> <span word="S">S</span>, <span word="and">and</span> <span word="the">the</span> <span word="other">other</span> <span word="number">number</span> <span word="is">is</span> <span word="selected">selected</span> <span word="from">from</span> <span word="T">T</span>. <span word="What">What</span> <span word="is">is</span> <span word="the">the</span> <span word="probability">probability</span> <span word="that">that</span> <span word="the">the</span> <span word="product">product</span> <span word="of">of</span> <span word="the">the</span> <span word="two">two</span> <span word="numbers">numbers</span> <span word="is">is</span> <span word="negative">negative</span>?</p><p> 【答案】1/2</p><p> 【思路】<span word="C">C</span>5 1<span word="C">C</span>3 1 / <span word="C">C</span>5 1<span word="C">C</span>6 1=1/2</p><p> 12、</p><p> <span word="What">What</span> <span word="is">is</span> <span word="the">the</span> <span word="function">function</span> <span word="of">of</span> <span word="the">the</span> <span word="curve">curve</span> <span word="above">above</span>?</p><p> <span word="y">y</span> = <span word="x">x</span>^3 - <span word="x">x</span>^2</p><p> <span word="y">y</span> = - <span word="x">x</span>^3 + <span word="x">x</span>^2</p><p> <span word="y">y</span> = - <span word="x">x</span>^3 +<span word="x">x</span></p><p> <span word="y">y</span> = <span word="x">x</span>^3 - <span word="x">x</span></p><p> <span word="y">y</span> = <span word="x">x</span>^3 + <span word="x">x</span></p><p> 【答案】</p><p> 【思路】根据图形可以知道应该找与<span word="X">X</span>轴有三个交点，也就是<span word="y">y</span>等于0时可以解出三个实根的方程。排除、、，因为只有两个实根，也是有两个实根，只有一个实根，只有是对的。又可以通过增减函数来排除，图形告诉我们<span word="X">X</span>向正无穷方向增加，<span word="Y">Y</span>的值也随之增加，从某点开始为增函数，再看方程明显从某点开始后为减函数，因此是对的。</p><p> 分页标题#<span word="e">e</span>#</p><p> 13、0-50中，被3整除余1的数有多少个?</p><p> 【答案】有17个</p><p> 【思路】0=3<span word="x">x</span>+1=50 <span word="x">x</span>=0.16</p><p> 14、<span word="N">N</span> <span word="is">is</span> <span word="the">the</span> <span word="sum">sum</span> <span word="of">of</span> <span word="the">the</span> <span word="first">first</span> <span word="K">K</span> <span word="consecutive">consecutive</span> <span word="positive">positive</span> <span word="integers">integers</span>, <span word="where">where</span> 101=150. <span word="What">What</span> <span word="is">is</span> <span word="the">the</span> <span word="sum">sum</span> <span word="of">of</span> 1/<span word="N">N</span>?</p><p> 【答案】2</p><p> 【思路】把<span word="first">first</span> <span word="consecutive">consecutive</span> 理解为是从1开始到<span word="k">k</span> 的数列。</p><p> <span word="N">N</span>=<span word="K">K</span>/2</p>
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