options: Statistics & Probability: students learn to analyze and produce data distributions, and build understanding of univariate and bivariate data. They learn to interpret data, make statistical inferences, justify conclusions, understand rules of probability, and use probability to make decisions.

Number & Operations in Base Ten: students learn to work with the base-ten system and build place value understanding.

Ratios & Proportional Relationships: students learn to recognize, describe, represent, and reason with ratios, rates, proportional relationships, and percent.

Geometry: students learn to classify geometric figures by their properties, and understand and compare the relationships between them. Students develop and use formulas to compute lengths, areas, and volumes, and they use transformations to generate new shapes and compare existing ones. Geometry can be studied with and without coordinates.

Functions: students learn to define, use, and evaluate functions to model relationships between quantities.

Modeling: students learn to choose and use appropriate mathematics and statistics to analyze real-world empirical situations, improve decisions, and report on their conclusions and the reasoning behind them.

Number & Operations - Fractions: students learn to understand fractions as numbers and may work with them using addition, subtraction, multiplication, and division.

Counting & Cardinality: students learn to know number names and the count sequence, count to tell the number of objects, and compare numbers.

Measurement & Data: students learn to work with data and measure attributes such as time, money, length, area, and volume. They may learn to compare measurements to operations and convert between different units of measure.

Number Systems and Quantity: students learn to understand the complex number system and reason quantitatively.

Operations & Algebra: students learn to solve problems using algebraic thinking and operations such as addition, subtraction, multiplication, and division. They may learn to identify and explain arithmetic patterns, evaluate or manipulate numerical expressions, and reason with equations and inequalities.
problem_activity: Activity
The goal of this activity is for students to recognize rewriting a quadratic expression from standard form to vertex form essentially entails completing the square.
Students had quite a bit of experience completing the square, mostly in the context of solving equations, in which they know to add or subtract the same number from both sides of an equation to keep the equation true. Here students are dealing with expressions and need to be careful to keep each expression equivalent to the original. If they add a number to the expression, they need to remember to subtract the same number to keep the value of the expression unchanged.
Launch
Arrange students in groups of 2. Give students quiet time to think about the first two questions and then time to share their thinking with a partner.
Pause for a class discussion after the second question and invite one or more students to demonstrate their strategy. Highlight approaches that involve completing the square. If no students took that approach, display and discuss the following:
\(\displaystyle \begin {align} &x^2 - 6x + 2\\ &x^2 - 6x + 9 - 9 + 2 \\&(x - 3)^2 - 7 \end {align}\)
Then, ask students to proceed with the rest of the activity. Provide access to devices that can run Desmos or other graphing technology.
Representation: Internalize Comprehension.
Use color and annotations to illustrate student thinking. As students share their reasoning about how to convert standard form back into vertex form, scribe their thinking on a visible display. Use annotations and labels to show the structure of the steps using the form included in the launch. For example, labeling the first step as “standard form,” labeling +9 as “add nine to complete the square,” and drawing an arrow to the -9 and labeling it as “keeping it equivalent.” Continue to add in any key phrases students contributed that illustrate the steps.
Supports accessibility for: Visual-spatial processing; Conceptual processing
Student Facing
Here are two expressions in vertex form. Rewrite each expression in standard form. Show your reasoning.
\((x+5)^2+1\)
\((x-3)^2-7\)
Think about the steps you took, and about reversing them. Try converting one or both of the expressions in standard form back into vertex form. Explain how you go about converting the expressions.
Test your strategy by rewriting
\(x^2+10x+9\)
in vertex form.
Let’s check the expression you rewrote in vertex form.
Use graphing technology to graph both
\(x^2+10x+9\)
and your new expression. Does it appear that they define the same function?
If you convert your expression in vertex form back into standard form, do you get
\(x^2+10x+9\)
?
Student Response
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Anticipated Misconceptions
Some students may wonder why they need to both add and subtract a number from the standard form expression in order to complete the square. In previous lessons, students completed the square while solving an equation, often adding the same number to each side of the equal sign to maintain equality. Here, there is no equal sign. Emphasize that each move must generate an equivalent expression. Show a few expressions such as 5,
\(5+0\)
,
\(5-2+2\)
,
\(5+7-7\)
,
\(5+8\)
, and
\(5+8-3\)
. Ask them which ones are equal to 5. Next, ask them to write 2 more expressions that include the number 5 and also equal 5. Encourage students to notice that the sum of the numbers excluding 5 must be 0.
Activity Synthesis
Invite students to share their graph and response to the last question. Emphasize that while graphing is a quick way to check whether two expressions define the same function, it is not always reliable. If we make an algebraic error, the graph would almost certainly show it. But having two graphs that
appear to be
identical does not
prove
that two expressions are indeed equivalent. We can only be sure that two expressions define the same function by showing equivalence algebraically. For example, when students convert the expression in vertex form back to standard form, does it produce the original expression?
Make sure students understand that whatever operation is performed on an expression to complete the square, it should not change the value of the expression. Adding opposites (for example, 9 and -9, or -25 and 25), or adding and subtracting the same number, has the effect of adding 0, which keeps the original and the transformed expressions equivalent.


correct_option_index: 10