GRE数学考生回忆（10）
<p> 51、问一个公司一年的<span word="revenue">revenue</span>增加了多少~</p><p> <span word="A">A</span>. 一年的<span word="expense">expense</span>增加了25%</p><p> <span word="B">B</span>.一年的<span word="gross">gross</span> <span word="profit">profit</span>减少了6%</p><p> <span word="revenue">revenue</span> = <span word="gross">gross</span> <span word="profit">profit</span> - <span word="expense">expense</span></p><p> 条件1+条件2)</p><p> 设以前<span word="revenue">revenue</span> = <span word="gp">gp</span><span word="ex">ex</span></p><p> 现在为<span word="revenue">revenue</span>= 0.94<span word="gp">gp</span>1.25 <span word="ex">ex</span></p><p> 差值为：-0.06<span word="gp">gp</span>0.25<span word="ex">ex</span> 初值不知，求解不出 选<span word="E">E</span></p><p> 52、问是否<span word="x">x</span>^2<span word="x">x</span></p><p> 0</p><p> <span word="x">x</span>^3<span word="x">x</span></p><p> <span word="DS">DS</span>,<span word="x">x</span>^2</p><p> <span word="x">x</span>2-<span word="x">x</span> = <span word="x">x</span></p><p> 条件1)0</p><p> 条件2)<span word="x">x</span>3<span word="x">x</span> 得 <span word="x">x</span>0</p><p> 分类讨论 当<span word="x">x</span>0时：1 <span word="or">or</span> <span word="x">x</span>-1 交集为：<span word="x">x</span>1</p><p> 此时<span word="x">x</span>0 确定</p><p> 当<span word="x">x</span>0时： 0 , -1</p><p> 此时<span word="x">x</span>0 确定 选D 选A 方法类同</p><p> 53、<span word="y">y</span>=<span word="x">x</span>^2+2<span word="x">x</span>-8,<span word="P">P</span>点是这个曲线与<span word="x">x</span>轴正半轴的焦点,<span word="Q">Q</span>点是这个轴与<span word="y">y</span>轴的交点,问,直线<span word="PQ">PQ</span>满足下列哪一条曲线方程? 令<span word="y">y</span>=0, <span word="x">x</span>2+2<span word="x">x</span>-8==0,所以<span word="x">x</span>=2 <span word="or">or</span> <span word="x">x</span>=-4,因为是正半轴,所以<span word="P">P</span>点的坐标为 令<span word="x">x</span>=0,<span word="y">y</span>=-8,所以<span word="Q">Q</span>点的坐标为 所以,方程<span word="y">y</span>=4<span word="x">x</span>-8</p><p> 54、<span word="taxi">taxi</span>走了<span word="d">d</span> <span word="miles">miles</span>.收费的公式是:1.9美元/<span word="mile">mile</span>, 外加每分钟0.4美元. 如果这个<span word="taxi">taxi</span>最后收了<span word="c">c</span> 美元,请问这个<span word="taxi">taxi</span>走这<span word="d">d</span> <span word="mile">mile</span>的平均速度是多少? 收费: <span word="c">c</span>=1.9<span word="d">d</span> + 0.4 60<span word="t">t</span> 所以,<span word="t">t</span>=/24 所以最后平均速度= <span word="d">d</span>/<span word="t">t</span> = 24<span word="d">d</span>/</p>
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