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<h3>Warm Up (5 minutes)</h3>
<p>This warm up prompts students to carefully analyze and compare quadratic expressions. The activity also enables the teacher to hear the terminology students know and how they talk about characteristics of the different forms of expressions.</p>
<p>As students discuss in groups, listen for rationales that are based on the structure of the expressions. Select those students or groups to share their thinking during class discussion.</p>
<h4>Launch</h4>
<p>Arrange students in groups of two to four. Display the expressions for all to see. Give students quiet time to think individually and then time to share their thinking with their small group. In their small groups, ask each student to share their reasoning about why a particular item does not belong, and together find at least one reason each item doesn't belong.</p>
<h4>Student Activity</h4>
<p>Examine the four expressions below. Which one doesn't belong?</p>
<ol class="os-raise-noindent" type="A">
  <li>\((x + 4)(x &minus; 3)\)</li>
</ol>
<ol class="os-raise-noindent" start="2" type="A">
  <li>\(3x^2 &minus; 8x + 5\)</li>
</ol>
<ol class="os-raise-noindent" start="3" type="A">
  <li>\(x^2 &minus; 25\)</li>
</ol>
<ol class="os-raise-noindent" start="4" type="A">
  <li>\(x^2 + 2x + 3\)</li>
</ol>
<p>There are many possible answers for which equation does not belong in a group with the others. Determine which equation you think should be eliminated and explain your reasoning.</p>
<p><strong>Answer:</strong> </p>
<p>Equation A: The only expression that is not in standard form. Or, when written in standard form, it is the only one that has an even number for the constant term.</p>
<p>Equation B: The only expression in standard form that has a leading coefficient other than 1.</p>
<p>Equation C: The only expression in standard form that doesn't have three terms. It is the only one without a linear term.</p>
<p>Equation D: The only expression in standard form that can't be written in factored form. It is prime.</p>
<h4>Activity Synthesis</h4>
<p>Ask each group to share one reason why a particular expression doesn't belong. Record and display the responses for all to see. After each response, ask the class if they agree or disagree. Since there is no single correct answer to the question of which one does not belong, attend to students' explanations and ensure the reasons given are correct.</p>
<p>During the discussion, ask students to explain the meaning of any terminology they use, such as standard form, factored form, linear term, or coefficient. Also, press students on unsubstantiated claims. For example, if they claim that B is the only one that cannot be written in factored form, ask them to show how they know.</p>