北京卷2004年高考题极富特色,第8题、第20题尤为突出.第8题为选择题形式,既考察基本概念,更考察理解学习能力,分析判断能力,是少见的好题.这里先将第8题及某书给出的解析抄录如下:8.函数f(x)=x,x∈P,-x,x∈M.其中,P,M为实数集R的两个非空子集.又规定f(P)={y|y=f(x),x∈P},f(M)={y|y=f(x),x∈M}.给出 The 2004 Beijing college entrance examination question is extremely characteristic. The 8th and 20th questions are particularly prominent. The 8th question is a multiple-choice question. It is not a good idea to examine the basic concepts, investigate and understand the ability to learn, and analyze and judge the ability. First copy the analysis given in the 8th question and the book as follows: 8. The function f (x) = x, x ∈ P, -x, x ∈ M. Among them, P, M are two non-empty sub-sets of the real number R Set. Also specified f (P) = {y | y = f (x), x ∈ P}, f (M) = {y | y = f (x), x ∈ M}.