新版GRE数学复习重要考点:Sum of Arithmetic ProGREssion
The sum of n-numbers of an arithmetic proGREssion is given by
S=nxdn/2
where x is the first number and d is the constant increment.
example:
sum of first 10 positive odd numbers:101+2109/2=10+90=100
sum of first 10 multiples of 7 starting at 7: 107+7109/2=70+315=385
remember:
For a descending AP the constant difference is negative.
由于美国数学基础教育的难度增加导致数学考试越来越难,但新GRE数学复习考点都是高中时候学到的知识点,考生不要过于紧张,把基本概念弄明白,再记住一些新版GRE数学必备的词汇,那么相信新版GRE数学应该没有问题。
AP
Average of n numbers of arithmetic proGREssion is the average of the smallest and the largest number of them. The average of m number can also be written as x + d/2.
Example:
The average of all integers from 1 to 5 is /2=3
The average of all odd numbers from 3 to 3135 is /2=1569
The average of all multiples of 7 from 14 to 126 is /2=70
remember:
Make sure no number is missing in the middle.
With more numbers, average of an ascending AP increases.
With more numbers, average of a descending AP decreases.
AP:numbers from sum
given the sum s of m numbers of an AP with constant increment d, the numbers in the set can be calculated as follows:
the first number x = s/m - d/2,and the n-th number is s/m + d/2.
Example:
if the sum of 7 consecutive even numbers is 70, then the first number x = 70/7 - 2/2 = 10 - 6 = 4.
the last number is 70/7+2/2=10+6=16.the set is the even numbers from 4 to 16.
Remember:
given the first number x, it is easy to calculate other numbers using the formula for n-th number: x+
AP:numbers from average
all m numbers of an AP can be calculated from the average. the first number x = c-d/2, and the n-th number is c+d/2, where c is the average of m numbers.
Example:
if the average of 15 consecutive integers is 20, then the first number x=20-1/2=20-7=13 and the last number is 20+1/2=20+7=27.
if the average of 33 consecutive odd numbers is 67, then the first number x=67-2/2=67-32=35 and the last number is 67+2/2=67+32=99.
Remember:
sum of the m numbers is cm,where c is the average.
以上是为大家整理的新GRE数学重要考点知识,希望能给新GRE考生带来一定的帮助。
雅思写作词汇分类汇总:工作类
中国学生雅思写作的四大通病
雅思写作通病之完不成写作任务
雅思9分范文:关于大学教育
雅思写作通病之词汇贫乏
雅思写作三要素
雅思议论文写作如何得高分
雅思写作词汇分类汇总:文化类
雅思写作名师答疑:名人名言会有用吗
雅思大作文点评:多文化社会的优缺点
雅思写作词汇分类汇总:动物保护类
雅思写作五大误区:光看范文而不写
老外的雅思9分例文又一力作
雅思大作文点评:是否应纳税?
雅思写作词汇分类汇总:媒体类
雅思7分作文范文
雅思写作词汇分类汇总:社会类
雅思大作文点评:学生是否应上私立中学?
雅思写作要避免语法错误
雅思作文权威点评:养宠物的利弊
雅思写作评分标准及考生应试策略
雅思写作通病之缺乏连贯性
雅思大作文点评:解决城市住房短缺只能靠政府?
雅思写作词汇分类汇总:交通类
雅思大作文点评:手机问题
雅思写作要避免语法错误 调整思维方式
雅思剑八写作解析之二:出题类型有变
雅思大作文点评:大学男生女生是否应一样多?
雅思写作常用词汇总结
雅思9分例文:人口与环境
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |