Term

　　A product of coefficients and any number of variables with exponents is called a term. Terms that have the same variables with identical exponents for each variables are called like terms.

　　Example:

　　3x,axy,4x2yz are terms. 3x+2 is not term: it is a sum of two terms.

　　3x2y and 7x2y are like terms since both have the same variables x and y with identical exponents: 2 for x and 1 for y.

　　Remember:

　　There cannot be any addition or subtraction in a single term.

　　Since multiplication is associative, rearrangements of variables does not change a term:3xy is same as 3yx.

　　3x2y and 7xyx are like terms.

　　GRE數(shù)學(xué)考點介紹：Conditional

　　Conditional

　　Probability of event A conditioned on the fact that event B has happened is called the conditional probability and written as P(AIB).

　　P(AIB)=Probability Both A and B happens/ Probability B happens.

　　Example:

　　A six-sided die with faces from 1 to 6 is rolled twice. What is the probability that the face 5 turned up on first try given that the sum of the two faces is 9?

　　P(sum of faces is 9)=4/36=1/9.

　　P(face 5 turns up on the first try and sum is 9)=(1/6)*(1/6)=1/36.

　　P(face 5 turned up on first try given sum is 9)=(1/36)*(1/9)=1/4

　　Remember:

　　If P(AIB)=P(A),then two events A and B are independent, that is occurrence of one does not influence the other