1、mode
一堆数中出现频率最高的一个或几个数,例如: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,例如:range of 1,1,2,3,5 is 5-1=4
3、mean
arithmatic mean,geometric mean
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,例如: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。例如: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,例如:standard variation of 0,2,5,7,6 is6.8
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,其中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=-1
10. 三的倍数的特点:所有位数之和可被3整除。
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