Substitution

　　Substitution is a method where one or more variables in an expression is replaced by numbers or another set of variables.To evaluate an expression specific numbers are used as substitute. To express in terms of another set of variables, variables are replaced by the new set of variables.

　　Example:

　　If x=3, then 2x2+4x+1 can be evaluated by substituting 3 for x.

　　Replacing all x by 3, we get 2*32+4*3+1=31.

　　If x=2+y, then x2-3 can be expressed in terms of y by replacing all x by (2+y):(2+y)2-3=y2+4y+1.

　　Remember:

　　Do not forget to replace all occurrences of the variable.

　　After substitution the variable does not appear anywhere in the expression.

　　有一部分考生认为新GRE数学具有一定的难度，这其中的原因是由于考生在复习时没有把新GRE数学的基础打牢。想要新GRE数学考好，复习的时候一定要把基本概念和重要考点都弄扎实。祝大家都能取得理想成绩!

编辑：张雨

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