GMAT数学备考资料：费费数学宝典详解版(六)
<p> 11、<span word="x">x</span>^2+<span word="x">x</span>-60，问：<span word="x">x</span>=?</p><p> <span word="x">x</span>是自然数;</p><p> -2</p><p> 【答案】<span word="A">A</span></p><p> 【思路】</p><p> <span word="x">x</span>^2+<span word="x">x</span>-6 -3与2是该一元二次方程的两个根,也就是该函数图像与<span word="X">X</span>轴交于和。<span word="x">x</span>^2+<span word="x">x</span>-60，则-3</p><p> <span word="x">x</span>为自然数，则与上述<span word="x">x</span>值域有交集，得出<span word="x">x</span>为小于2的自然数，<span word="x">x</span>=1。充分;</p><p> -2</p><p> 12、数列{7, 6, 9, 10, 4}加入3，7，12，哪个使得新的数列<span word="median">median</span>=<span word="mean">mean</span>?</p><p> <span word="I">I</span>. 3</p><p> <span word="II">II</span>. 7</p><p> <span word="III">III</span>. 12</p><p> 【答案】3和12</p><p> 【思路】</p><p> 数列加3，新数列为{3,4,6,7, 9,10}, <span word="median">median</span>=/2=6.5，<span word="mean">mean</span>=39/2=6.5, <span word="I">I</span>可以;</p><p> 数列加7，新数列为{4,6,7, 7,9,10}, <span word="median">median</span>=7，<span word="mean">mean</span>=43/67.2, <span word="II">II</span>不可以;</p><p> 数列加12，新数列为{4,6,7, 9,10,12}, <span word="median">median</span>=/2=8，<span word="mean">mean</span>=48/6=8, <span word="III">III</span>可以。</p><p> 13、-3</p><p> 【答案】|<span word="x">x</span>+1|2</p><p> 【思路】-3</p><p> 14、<span word="A">A</span>1=2, <span word="A">A</span>2=3, <span word="A">A</span>3=<span word="A">A</span>1<span word="A">A</span>2, <span word="A">A</span>4=<span word="A">A</span>1<span word="A">A</span>2<span word="A">A</span>3,，若<span word="An">An</span>=<span word="t">t</span>，那么<span word="An">An</span>+2=?</p><p> 【答案】<span word="t">t</span>^4</p><p> 【思路】</p><p> 根据条件可得：<span word="A">A</span>=<span word="A">A</span>1<span word="A">A</span>2<span word="A">A</span>3.<span word="AnA">AnA</span>; <span word="A">A</span>=<span word="A">A</span>1<span word="A">A</span>2<span word="A">A</span>3.<span word="AAn">AAn</span>;</p><p> <span word="An">An</span>=<span word="A">A</span>1<span word="A">A</span>2<span word="A">A</span>3.<span word="A">A</span>=<span word="t">t</span><span word="A">A</span>=<span word="An">An</span>^2, 同理可得<span word="A">A</span> =<span word="A">A</span>^2;</p><p> 代入则有：<span word="A">A</span> =<span word="An">An</span>^4=<span word="t">t</span>^4</p><p> </p>
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