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
; B% u k; J* S0 Y$ M; ` S=nx*dn(n-1)/2
! Z2 ]8 I2 L7 G9 N where x is the first number and d is the constant increment.
o5 p1 q# q4 U, c example:
O F1 ]0 ~9 _/ C }0 ?* I sum of first 10 positive odd numbers:10*1+2*10*9/2=10+90=100
$ }' G; i1 y- Y sum of first 10 multiples of 7 starting at 7: 10*7+7*10*9/2=70+315=385
$ s2 v' d& Y- n9 l1 O% v- }, V5 I9 _ remember:% ?% v! E0 z, z' O/ ^4 h' I* y n
For a descending AP the constant difference is negative., X! r* P( i/ Z) L8 @+ w
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。 |