Adding and Subtracting Monomials

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SWBAT add and subtract monomial and polynomial expressions.

Big Idea

This lesson uses a pre-assessment to determine student's understanding. The work is then differentiated based on student need.

Warm Up

5 minutes

Students should work individually on the add_monomials_warmup activity.  Based on each student's past experience with solving equations with combining like terms, s/he should be able to determine how to simplify the given expressions.  Once students have had an opportunity to complete all three questions, I will ask them to compare answers with a partner.  Students should discuss their individual answers and come to an agreement as to which are correct (MP3, MP6). I plan to choose three students who came up with the correct answers to post their answers on the board. 


5 minutes

The add_monomials_launch question asks students to justify the simplification of an expression (MP2). I plan to have students do a think-pair-share to discuss the stated result for simplifying the expression (MP3). When students are discussing their response, listen for pairs of students that are realizing which terms need to be combined.  

When students share out their justifications, I plan to call on students that have a less sophisticated justification first.  Then have others respond and add in their own ideas to make the justification stronger (MP3).


25 minutes

Next, I will have the students assess their understanding of the concept by taking the add_monomials_pre_assess.  This pre-assessment will only take about 5 minutes. I will have students can grade their own paper.  I emphasize to students that the grade is not important. I want them to practice identifying what misunderstandings they have that are causing them to come up with the incorrect answers.  

Once all of the students have finished the pre-assessment, I will put the answers up so that students can check their own papers (add_monomials_preassess_solutions).  I ask students to give themselves a score out of 4.  The practice portion of the lesson is differentiated so that all students have exercises at their own level to help build their conceptual and procedural knowledge (add_monomials_practice).  


5 minutes

At first, I ask students to work on the add_monomials_closure activity individually.  Students can reason about why this common misconception would not be true (MP2).  I expect students to use a variety of approaches such as:

  1. Plugging in a value for x
  2. Draw a picture of 3 x's and cross out one of the x's
  3. Explain based on the day's lesson that the variable stays the same and the coefficients are subtracted

I leave about 3 minutes at the end of class for students to share some of their responses. I plan to highlight creativity in student thinking and to let students respond to each other's ideas.