GRE数学考点：Substitution
<p> <span word="Substitution">Substitution</span></p><p> <span word="Substitution">Substitution</span> 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.</p><p> <span word="Example">Example</span>:</p><p> <span word="If">If</span> <span word="x">x</span>=3, <span word="then">then</span> 2<span word="x">x</span>2+4<span word="x">x</span>+1 <span word="can">can</span> <span word="be">be</span> <span word="evaluated">evaluated</span> <span word="by">by</span> <span word="substituting">substituting</span> 3 <span word="for">for</span> <span word="x">x</span>.</p><p> <span word="Replacing">Replacing</span> <span word="all">all</span> <span word="x">x</span> <span word="by">by</span> 3, <span word="we">we</span> <span word="get">get</span> 232+43+1=31.</p><p> <span word="If">If</span> <span word="x">x</span>=2+<span word="y">y</span>, <span word="then">then</span> <span word="x">x</span>2-3 <span word="can">can</span> <span word="be">be</span> <span word="expressed">expressed</span> <span word="in">in</span> <span word="terms">terms</span> <span word="of">of</span> <span word="y">y</span> <span word="by">by</span> <span word="replacing">replacing</span> <span word="all">all</span> <span word="x">x</span> <span word="by">by</span> :2-3=<span word="y">y</span>2+4<span word="y">y</span>+1.</p><p> <span word="Remember">Remember</span>:</p><p> <span word="Do">Do</span> <span word="not">not</span> <span word="forget">forget</span> <span word="to">to</span> <span word="replace">replace</span> <span word="all">all</span> <span word="occurrences">occurrences</span> <span word="of">of</span> <span word="the">the</span> <span word="variable">variable</span>.</p><p> <span word="After">After</span> <span word="substitution">substitution</span> <span word="the">the</span> <span word="variable">variable</span> <span word="does">does</span> <span word="not">not</span> <span word="appear">appear</span> <span word="anywhere">anywhere</span> <span word="in">in</span> <span word="the">the</span> <span word="expression">expression</span>.</p><p> 有一部分考生认为新<span word="GRE">GRE</span>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<span word="GRE">GRE</span>数学的基础打牢。想要新<span word="GRE">GRE</span>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!</p><p> </p><p> </p>
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