马上要考了 急！几道prep数学

lmf0801

马上要考了 急！几道prep数学
1  The numbers 75 can be  written as the sum of  the squares of 3 different positive intergers  What is the sum of these 3 intergers
17  16   15 14  13

2 Inx-yplane at what two points does graph of y=(x+a)(x-a)intersects the x-axis?
(1)  a+b=-1   (2)  the graph intersects the  y-axis  (0-6)

3 A certain library assess fines for overdue books as follow on the frist day that a book is overdue The total fine is 0.1$.For each addtional day  that a book is overdue the total fine is either increased by 0.3 or doubled whichever result  in the lesser amount that is the total fine for a book on forth day it is overdue
0.6            0.7              0.8              0.9            1.0
这道题我想问一下这个doubled 难道不是在上一次的本金+fine上进行doubled 的吗  难道只是按第一次的fine 0.1 doubled的吗
然后后面都是这个fine在相加？？？


4    Six countries in a certain region sent a total of 75represetive to an international congress . and no two counteries sent  the same numbers of representives of the six countries . if country A  sent the second  greatest numbers of representives did country A sent at least 10 representives?
(1)  One of six counteries sent 41 representives to congress
(2)  Country A sent fewer than 12 representives to congress


5    Hery purchase   3 items during a sale  he received a 20 present discount off the regular price of  the most expensive items and a 10 persent discount  off the regular price of each  of the  other items  was the toal amount of  the 3 discounts greater than 15 precent of the sum of the regular price of  the 3 items ?
(1)The regular price of the most expensive item was $50 and the regular of the next expensive item was $20
(2) the rugular price of the least expensive items was $15
求助这道题的翻译 ！！

lmf0801

但是答案给的是C 啊 两个加起来才充分 我觉得我是不是审题有点问题啊

yougushizi

没错没错，极对

这个第二题我还有点疑问 题目是不是一定要确定与-x轴的交点？ 还是问这个抛物线和-X有截距？如果有截距的话第2个条件ab=-6说明了抛物线上与X轴两个交点一定在异侧 不就回答了这个问题么

-- by 会员 lmf0801 (2010/8/21 21:08:23)

yougushizi

sorry,sorry!下面这题又马虎了……

我发现这题根本就没让求交点……开口向上的抛物线和y的负半轴有交点，B就已经够了。
A不够，y=x^2-x+ab,还需要ab<1/4

刚才不好意思 第2 题发错了 是这样的、
2 Inx-yplane at what two points does graph of y=(x+a)(x+b)intersects the x-axis?

-- by 会员 lmf0801 (2010/8/21 20:28:06)

-- by 会员 yougushizi (2010/8/21 20:43:28)

lmf0801

这个第二题我还有点疑问 题目是不是一定要确定与-x轴的交点？ 还是问这个抛物线和-X有截距？如果有截距的话第2个条件ab=-6说明了抛物线上与X轴两个交点一定在异侧 不就回答了这个问题么

yougushizi

刚才不好意思 第2 题发错了 是这样的、
2 Inx-yplane at what two points does graph of y=(x+a)(x+b)intersects the x-axis?
(1)  a+b=-1   (2)  the graph intersects the  y-axis  (0 ,-6)
sorry,sorry!
我发现这题根本就没让求交点……开口向上的抛物线和y的负半轴有交点，B就已经够了。
A不够，y=x^2-x+ab,还需要ab<1/4


连列，
第三题 我想答案是不是意思就是
0.1+0.1*2*3     也就是后面每天的fine只按第一天基础上fine 即 后面每天double以后都是0.2这个每天都要比一下，不是一天就能看出来的。这题是你这样列，换个数可能就不是了。

-- by 会员 lmf0801 (2010/8/21 20:28:06)

fannybeibei

这是与X的交点，-b，—a
statement1：不充分
statement2：-6=ab
together, 求出2&-3
C

fannybeibei

额。。。第二题换题目了。。。
lz再等等。。。

fannybeibei

第二题，B
求a的值（这是与X的交点，+a，—a）
statement1：不充分
statement2：代入，a^2=6
那么就是正负根号6为交点，成立

lmf0801

刚才不好意思 第2 题发错了 是这样的、
2 Inx-yplane at what two points does graph of y=(x+a)(x+b)intersects the x-axis?
(1)  a+b=-1   (2)  the graph intersects the  y-axis  (0 ,-6)

第三题 我想答案是不是意思就是
0.1+0.1*2*3     也就是后面每天的fine只按第一天基础上fine 即 后面每天double以后都是0.2