After this lesson, students will be able to write the vertex form of a quadratic function: y = a(x − h) + k. They will know what the parameters a, h, and k have to do with the graph of a parabola. They will be able to look at the equation and instantly see the vertex, which gives them the minimum or maximum value of the graph. Students will be able to sketch graphs of parabolas quickly using the vertex form and will be able to write the equation given the graph. This lesson familiarizes students with the vertex form of a parabola to prepare them to be successful in the next two lessons. In addition, students need to see a purpose for what they are learning, and since quadratic relationships and parabolas happen all around us, they will be more motivated to learn the content. After this lesson, students will understand that the vertex form of a parabola can be more useful than the standard form, and this will set them up to be successful in the following lessons.
Students should begin this lesson by reviewing concepts of minimum, maximum, vertex, and axis of symmetry as they relate to parabolas. Hand out copies of the Entrance Ticket for students to complete (MA221_Entrance Ticket.doc).
ThinkPairShare
“Think about the quadratic function y = x^{2} + 6x + 8. [IS.3  Struggling Learners] Without graphing it, how could you determine the coordinates of the vertex?”
For the first minute, tell students to keep their pencils down. For the second minute, have them write their ideas of how to find the vertex. When time is up, pair students to share their thoughts with each other. Bring the class together and write all the ideas on the board.
If students struggle coming up with ideas, put the graph on the board.
“We know that we can look at the graph and see where the vertex is. But algebraically, how could we determine the coordinates?”
Pause for student ideas and responses.
“What is so special about the vertex? What are the characteristics of the vertex?” [IS.4  All Students] Students might mention the vertex is either the lowest (minimum) or highest (maximum) point on the graph; the vertex is in the middle.
“This lesson is going to introduce us to a new way of writing quadratic functions.”
Activity 1: The Human Parabola [IS.5  All Students]
Take students to a large area (hallway, cafeteria, gym, outside). Do not allow calculators, [IS.6  Struggling Learners] as students should be able to do the math in their head or on a piece of paper. Place the ropes on the floor as the x and yaxes. Place students into groups of 5. They are going to be the coordinates of a parabola.

The first group is going to be y = x^{2}. One student should be the vertex while the other students represent two points on each side of the vertex (example: x = −2, −1, 1, and 2). [IS.7  All Students] Students will be “connected” with a string.

The second group is going to be y = (x – 4)^{2} and then y = (x + 4)^{2}. They should use the same xvalues that the first group did.

The third group is going to be y = x^{2} + 1 and then y = x^{2} – 1.

The fourth group is going to be y = −x^{2}. Some students may come up with different answers. Some students might say that when x = 2, y is 4 while others would say y is −4. This is a good time to discuss order of operations.

The fifth group is going to be y = 3x^{2} and then .

Any students not in a group will write everyone’s observations after each equation is graphed. Have them write on poster paper (one for each equation) so you can hang the results in the classroom after the activity.

Group #1 is always going to stay on the axes. Group #2 will graph their first equation and the entire class should discuss their observations.

Some questions to ask after each new parabola is graphed are: “What is the difference between the original parabola (y = x^{2)} and the new one? [IS.8  All Students] (horizontal shift of 4 units right; horizontal shift of 4 units left; vertical shift of 1 unit up; vertical shift of 1 unit down; reflection across the xaxis; vertical stretch by a factor of 3; vertical compression by a factor of 2) What are the coordinates of the vertex of the new parabola? [(0, 4); (0, 4); (0, 1); (0, 1); (0, 0); (0, 0); (0, 0)] Are the shapes of the parabolas the same?” (The shapes are essentially the same, except for the last two which are compressions/stretches, but still retain essentially the same parabolic shape.)

Group #2 will graph the second equation with discussion to follow. Do this until all equations have been graphed and discussed. Go back to the classroom and hang the posters at the front of the class.

“Can anyone draw any conclusions from the Human Parabola activity? If not, that is okay; we are going to do another activity that may help you understand.”

Activity 2: Individual and Pair Work
Hand out the Parabola Exploration Worksheet (MA221_Parabola Exploration Worksheet.doc).
“Using your graphing calculator and observations from our first activity, explore what happens to a parabola when the equation changes.” [IS.9  All Students]
Have students work on this worksheet on their own for a while and then have them work in pairs.
“What are some things you noticed that happened to the original graph of y = x^{2} when the equation was written a little differently?” Discuss the worksheet with the class. [IS.10  All Students]
Write the vertex form of the quadratic equation on the board: y = a(x − h)^{2 }+ k. Discuss how the graph of the parabola is affected as the values of a, h, and k are changed.
“The vertex of a parabola is at point (h, k). In the equation y = (x − 4)^{2} + 3, the vertex is at point (4, 3). What happens if we change the 3 to a bigger number?” (The vertex shifts up.) “What happens if we change the (x − 4) to (x + 4)?” [IS.11  All Students] (The vertex shifts left eight spaces.)
Discuss with students how the parabola is affected with changes in the value of a.
Ask the fifth group (from Activity 1) how its parabola changed between y = 3x^{2} and . (y = 3x^{2} was skinnier than , or that as a got smaller the parabola got wider)
“How does the parabola change if a is negative?” Wait for responses. (graph gets skinnier, turns upside down, etc.) Ask group 4 (from Activity 1) how the equation y = −x^{2} looked once it was graphed. (The parabola opened facing down.) “That’s right. When a is positive, the parabola opens upward; when a is negative it opens downward.” Another way of saying this is “When a is positive the vertex is the bottom of the parabola. When a is negative the vertex is the top of the parabola. Is it a minimum or maximum point?”
Distribute the graphic organizer (MA221_Graphic Organizer.doc). [IS.12  Struggling Learners] Help students fill in the blanks for the missing parameters of the vertex form. A key is provided for the graphic organizer (MA221_Graphic Organizer KEY.doc). Note that the minimum and maximum occurs at the vertex. The maximum and minimum value is the ycoordinate.
Remind students how to determine/locate the xvalue of the vertex. Students need to first find the x – h part of the quadratic function in the given equation; since there is a minus sign in front of the h, the xvalue of the vertex is always the opposite of what is in parentheses. If the equation has (x – 3)^{2}, then the xvalue of the vertex is 3 (NOT negative 3). If the equation has (x + 3)^{2}, then the xvalue of the vertex is −3. Also remind students how to determine/locate the yvalue of the vertex: look for k.
Activity 3: MiniWhiteboards
Place the following equations on the board. One equation at a time, have students write the vertex of each parabola on their whiteboard. [IS.13  Struggling Learners] Give them a simple yes or no. They can go on to the next equation if they get a yes; if they get a no, they need to try again.


1. y = x^{2} + 3

2. y = (x − 5)^{2}

3. y = −x^{2}

4. y = 3(x + 2)^{2} − 1

5. y = (x − 3)^{2} + 4



6. y = (x + 8)^{2} + 11

7.

8. y = − (x + 4)^{2} − 3

9. y = (x + 2)^{2}

10. y = −x^{2} − 4

Answer Key:

1. (0, 3)

2. (5, 0)

3. (0, 0)

4. (−2, −1)

5. (3, 4)


6. (−8, 11)

7. (9, −12)

8. (−4, −3)

9. (−2, 0)

10. (0, −4)
Example:
Gather the class together and ask, [IS.14  Struggling Learners] “How many of you have tried skateboarding or rollerblading? Have you ever seen a ramp the skaters use to do tricks, called a halfpipe?” Show picture of a halfpipe (MA221_Half Pipe.doc). “What does the shape remind you of?” (parabola)
“Today you are going to do the math behind designing a halfpipe by writing the equations of the parabolic path halfpipes make. Let’s take a look.” Show the halfpipe as parabola picture (MA221_Half Pipe.doc).
“How would we begin writing the equation for this parabola? What are some things we learned.” (Students should come up with vertex or stretch factor; if not, give them some hints.) [IS.15  All Students]
Put the Steps for Writing Equation worksheet (MA221_Steps for Writing Equation.doc) on the board or document camera for students to copy down as notes. “Here we have a halfpipe. It is 20 feet long and 8 feet tall. In the middle is a parabola. We are going to write the equation for this parabola.” Point out the parabola and dimensions of the halfpipe on the board.
“The first thing we are going to do is turn the picture into a graph by adding x and y axes. These can be placed anywhere, but today we’re going to put them at the bottom left of the drawing.” Add or point out axes on the drawing.
“Now we are going to label some points on the graph. What points can we label?” Wait for responses. Responses may include the origin, vertex of the parabola, etc.
“Let’s go on to the next step. We can label the origin, since we know that it is always at (0, 0). We can see that the vertex of the parabola is one foot up from the x axis and in the middle of the 20 foot halfpipe. So we can tell that the vertex is at point (10, 1). We can also see one of the points on the parabola is at the top of the halfpipe which is eight feet tall and two feet in from the edge, making it point (2, 8).”
“We are going to label the origin, the parabola’s vertex and the point on the parabola.” Label or point out origin (0, 0); vertex (10, 1); and point on parabola (2, 8).
“We can use these points to find the equation of the parabola. The first step is to put the vertex (10, 1) into the vertex form of the equation.” Write the vertex form of a parabola on the board y = a(x – h)^{2} + k on the board. Then replace h with 10 and k with 1, resulting in equation y = a(x – 10)^{2} + 1.
“We have completed almost all of the equation, only the stretch factor, a is missing. We will do that by substituting for our other point on the parabola, (2, 8), for x and y.” Write the equation, 8 = a(2 – 10)^{2} +1 on the board. [IS.16  All Students]
“Now we solve for a.”
 8 = a(2 – 10)^{2} +1
 7 = a(8)^{2}
 7 = a(64)
 = a
 “We put a back into the vertex form of a parabola and we have the equation for the halfpipe.” Write equation y = (x – 10)^{2} + 1 on the board.
Activity 4: Group Work [IS.17  All Students]
Separate the class into groups of three to five. Tell students to keep their notes out for reference. They are going to solve the following two problems. Each person in the group has to place their axes in a different spot. Students will write equations modeling the two problems. When everyone has completed the task, they will pass their equations around to check each other’s work.
Problem #1: Lucy was at the zoo watching the spider monkeys play in the trees. She read that spider monkeys usually stay in trees that reach 150 feet into the air and can swing between trees that are 80 feet apart. [IS.18  All Students] The bottom of their swing is 60 feet off the ground.
Problem #2: A football was on the ground, and Tony decided to give it a good kick. It landed 100 feet from where he kicked it. While in the air, it reached a height of 125 feet.
Ask the class the following questions for each of the problems above:
“What is one similarity among all of your equations?” Students should notice that the stretch factor is the same in all the equations. [IS.19  All Students]
“What is one difference among all of your equations?” Students should notice that the coordinates of the vertex are different in each equation.
“What is one way to check and see that your equations represent the same parabola?” (Compare the values of a.)
Activity 5: Individual Work
“For each problem, find the equation of the parabola that has the specified vertex and that goes through the given point.” [IS.20  All Students]

1. Vertex (2, 1) and has point (4, 13)

2. Vertex (−4, −2) and has point (6, −27)

3. Vertex (6, −3) and has point (0, −75)

4. Vertex (−1, 5) and has point (−3, 7)


Answer Key

y = 3(x – 2)^{2} +1

y =

y = 2(x – 6)^{2} – 3

y =
Have students write their answers on the board and discuss any issues with confusion or difficulty.
Hand out the Lesson 1 Exit Ticket (MA221_Lesson 1 Exit Ticket.doc and MA221_Lesson 1 Exit Ticket KEY.doc) to evaluate students’ understanding.
Routine: Group and partner work is used throughout so that students can help each other. Emphasis should be placed on communicating mathematical ideas with specific vocabulary words appropriate to the concepts. The lesson requires accurate notetaking skills to enhance the learning experience while creating a useful resource (notes). [IS.21  Struggling Learners]
Alternate Lesson Suggestions: This lesson can be covered in two days if so desired. If you wish to cover this lesson over two days, the suggested method is to cover up to and including Activity 3 the first day, then use the Example to reintroduce the topic, then cover Activities 4 and 5 the next day.
Extension: