搜题请搜索小程序“爱下问搜题”
问题 填空题

过点C（3，4）且与x轴，y轴都相切的两个圆的半径分别为r1，r2，则r1r2=______．

答案

由题意得：满足与x轴，y轴都相切的圆的圆心在第一象限，

设圆心坐标为（a，a），则半径r=a，

∴圆的方程为（x-a）2+（y-a）2=a2，

又C（3，4）在此圆上，

∴将C的坐标代入得：（3-a）2+（4-a）2=a2，

整理得：a2-14a+25=0，

∵r1，r2分别为a2-14a+25=0的两个解，

∴r1r2=25．

故答案为：25

填空题

烘焙菊苣(咖啡代用品)
查看答案
单项选择题

For many people today, reading is no longer relaxation. To keep up their work they must read letters, reports, trade publications, interoffice communications, not to mention newspapers and magazines: a never ending flood of words. In (1) a job or advancing in one, the ability to read and comprehend (2) can mean the difference between success and failure. Yet the unfortunate fact is that most of us are (3) readers. Most of us develop poor reading (4) at an early age, and never get over them. The main deficiency (5) in the actual stuff of language itself—words. Taken individually, words have (6) meaning until they are strung together into phrases, sentences and paragraphs. (7) , however, the untrained reader does not read groups of words. He laboriously reads one word at a time, often regressing to (8) words or passages. Regression, the tendency to look back over (9) you have just read, is a common bad habit in reading. Another habit which (10) down the speed of reading is vocalization—sounding each word either orally or mentally as (11) reads.
To overcome these bad habits, some reading clinics use a device called an (12) , which moves a bar(or curtain) down the page at a predetermined speed. The bar is set at a slightly faster rate (13) the reader finds comfortable, in order to "stretch" him. The accelerator forces the reader to read fast, (14) word by word reading, regression and subvocalization practically impossible. At first (15) is sacrificed for speed. But when you learn to read ideas and concepts, you will not only read faster, (16) your comprehension will improve. Many people have found (17) reading skill drastically improved after some training. (18) Charlie Au, a business manager, for instance. His reading rate was a reasonably good 172words a minute (19) the training; now it is an excellent 1,378 words a minute. He is delighted that how he can (20) a lot more reading material in a short period of time.

A．some one
B．one
C．he
D．reader
查看答案