GRE数学大全:基本概念总结篇
一、数学基本概念
1、mode
一堆数中出现频率最高的一个或几个数
e.g. mode of 1,1,1,2,3,0,0,0,5 is 1 and 0
2、range
一堆数中最大和最小数之差
e.g. range of 1,1,2,3,5 is 5-1=4
3、mean
arithmatic mean
geometric mean n个数之积的n次方根
4、median
将一堆数排序之后,正中间的一个数,
或者中间两个数的平均数
e.g. median of 1,7,4,9,2,2,2,2,2,5,8 is 2
median of 1,7,4,9,2,5 is /2=6
5、standard error
一堆数中,每个数与平均数的差的绝对值之和,除以这堆数的个数
e.g. standard error of 0,2,5,7,6 is:
/5=2.4
6、standard variation
一堆数中,每个数与平均数之差的平方之和,再除以n
e.g. standard variation of 0,2,5,7,6 is: s
_ 2 2 2 2 2_
|_ ++++_|/5=6.8
7、standard deviation
就是standard variation的平方根
标准方差的公式:d^2=/n
d 为标准方差
8、三角形 余玄定理C^2=A^2+B^2-2ABCOSt t为AB两条线间的夹角
9、Y=k1X+B1,Y=k2X+B2,两线垂直的条件为K1K2=
10、三的倍数的特点:所有位数之和可被3整除
11、N的阶乘公式:
N!=123....N
且规定0!=1
例如
8!=12345678
12、 熟悉一下根号2、3、5的值
sqrt=1.414
sqrt=1.732
sqrt=2.236
13. ...2/3 as many A as B: A=2/3B
...twice as many... A as B: A=2B
14. a if only b: b-a
15. 数学常用术语
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