设x1，x2，是方程2x2-8x+5=0的两个根， A． B． C． D． E．2

两条平行直线l1、l2分别过点P(-2，-2)，Q(1，3)，并且这两条直线之间的距离是d，如果这两条直线各自绕点P、Q旋转并始终保持平行

甲、乙两人在环形跑道上跑步，他们同时从起点出发，当方向相反时每隔48秒相遇一次

一次运动会，A班参加人数和B班参加人数之比为5:4，C班参加人数和D班参加人数之比为25:9

某人乘长途客车中途下车，客车开走10min后，发现将一行李遗忘在客车上，情急之下

已知a，b，c为任意非零实数，则表达式可以取的值有______．

若实数a、b、c满足a:b:c=1:2:5，且a+b+c=24，则a2+b2+c2=______．

To combat the trap of putting a premium on being busy, Cal Newport, author of em>Deep Work/em>: em>Rules for Focused Success in a Distracted World/em>, recommends building a habit of "deep work"—the ability to focus without distraction. There are a number of approaches to mastering the art of deep work—be it lengthy retreats dedicated to a specific task; develop a daily ritual; or taking a "journalistic" approach to seizing moments of deep work when you can throughout the day. Whichever approach, the key is to determine your length of focus time and stick to it. Newport also recommends "deep scheduling" to combat constant interruptions and get more done in less time. "At any given point, I should have deep work scheduled for roughly the next month. Once on the calendar, I protect this time like I would a doctor's appointment or important meeting," he writes. Another approach to getting more done in less time is to rethink how you reprioritize your day—in particular how we craft our to-do lists. Tim Harford, author of em>Messy: The Power of Disorder/em> em>to Transform Our Lives/em>, points to a study in the early 1980s that divided undergraduates into two groups: some were advised to set out monthly goals and study activities; others were told to plan activities and goals in much more detail, day by day. While the researchers assumed that the well-structured daily plans would be most effective when it came to the execution of tasks, they were wrong: the detailed daily plans demotivated students. Harford argues that inevitable distractions often render the daily to-do list ineffective, while leaving room for improvisation in such a list can reap the best results. In order to make the most of our focus and energy, we also need to embrace downtime, or as Newport suggests, "be lazy." "Idleness is not just a vacation, an indulgence or a vice; it is as indispensable to the brain as vitamin D is to the body...[idleness] is, paradoxically, necessary to getting any work done," he argues. Srini Pillay, an assistant professor of psychiatry at Harvard Medical School, believes this counterintuitive link between downtime and productivity may be due to the way our brains operate. When our brains switch between being focused and unfocused on a task, they tend to be more efficient. "What people don't realize is that in order to complete these tasks they need to use both the focus and un focus circuits in their brain," says Pillay. The key to mastering the art of deep work is to ______.

若数列{an}由a1=2，an+1=an+2n(n≥1)确定，则a100的值是______。

等比数列｛an｝中，a3、a8是方程3x2+2x-18=0的两个根，则a4a7______。

一个两位数恰好等于它两位上的数字之和的2倍，这样的两位数共有 ．

如图，在四边形ABCD中，AB//CD，AB与CD的边长分别为4和8，若△ABE的面积为4

三个正数a，b，c的算术平均值为几何平均值为6，则下面各情况中不可能的为______．

已知等差数列{an}中的a1与a10是方程x2-3x-5=0的两个根

动点A在圆x2+y2=1上移动时，它与定点B(3

计算的值为 A． B． C． D． E．

小刚和小强赛跑情况如下图所示，则下列叙述正确的是______．

经过点A(3，2)的一条动直线L分别交x轴，y轴于M、N两点，Q是线段MN的中点

若不等式ax2+bx+c＜0的解为一2＜x＜3

有3个学校共订300份《人民日报》，每个学校至少订99份，至多订101份