gre数学考点之算数解析.

　　在gre数学复习时整理gre数学考点是对gre数学考试有很大帮助的，因为gre数学对于国内的学子来说不仅仅是公式还涉及到英文的词汇，和英文的算数，澳际小编为大家整理出了关于算数的考点。

　　Gre数学的难度有一部分是体现考查国内学子对于数学词汇的认识与理解，所以说在gre数学复习时，用英文去做题是必不可少的，下面澳际小编整理出的算数部分的gre数学考点，希望可以帮助大家。

　　gre数学考点1.Sum of Arithmetic Progression(等差数列求和)

　　The sum of n-numbers of an arithmetic progression is given by

　　S=nx*dn(n-1)/2

　　where x is the first number and d is the constant increment.

　　example:

　　sum of first 10 positive odd numbers:10*1+2*10*9/2=10+90=100

　　sum of first 10 multiples of 7 starting at 7： 10*7+7*10*9/2=70+315=385

　　remember:

　　For a descending AP the constant difference is negative.

　　gre数学考点2.AP(等差数列求平均数)

　　Average of n numbers of arithmetic progression (AP) is the average of the smallest and the largest number of them. The average of m number can also be written as x + d(m-1)/2.

　　Example:

　　The average of all integers from 1 to 5 is (1+5)/2=3

　　The average of all odd numbers from 3 to 3135 is (3+3135)/2=1569

　　The average of all multiples of 7 from 14 to 126 is (14+126)/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(m-1)/2,and the n-th number is s/m + d(2n-m-1)/2.

　　Example:

　　if the sum of 7 consecutive even numbers is 70, then the first number x = 70/7 - 2(7-1)/2 = 10 - 6 = 4.

　　the last number (n=m=7)is 70/7+2(2*7-7-1)/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+(n-1)

　　AP:numbers from average

　　all m numbers of an AP can be calculated from the average. the first number x = c-d(m-1)/2， and the n-th number is c+d(2n-m-1)/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*(15-1)/2=20-7=13 and the last number (n=m=15) is 20+1*(2*15-15-1)/2=20+7=27.

　　if the average of 33 consecutive odd numbers is 67, then the first number x=67-2*(33-1)/2=67-32=35 and the last number (n=m=33) is 67+2*(2*33-33-1)/2=67+32=99.

　　Remember:

　　sum of the m numbers is c*m,where c is the average.

　　gre数学考点3.Sequence of Numbers(序列)

　　A sequence is a set of numbers that follow a fixed pattern.The fixed pattern can be expressed by an equation or by a property.

　　Example:

　　A set of consecutive integers: 1,2,3,4,5(Fixed gap)

　　A set of consecutive even numbers:4,6,8,10,12 (Fixed gap)

　　A set of consecutive prime: 2,3,5,7,11(Fixed gap)

　　A set of consecutive power of 2:4,8,16,32,64(Fixed gap)

　　Remember:

　　A sequence can be in ascending or descending order.

　　以上就是澳际小编为大家整理的算数部分gre数学考点，可以看出分为等差数列求和、等差数列求平均数、序列，希望大家在平时的gre数学复习中多记一些，肯定对大家在gre数学考试中有帮助的，祝大家gre数学考试成功。