few_shots: 
Example 1:
Problem/activity:
Find the general solution for:
$${\mathrm{cos}\left({\pi\over2}+x\right)=\mathrm{tan}{\pi\over4}}$$


Concept/skill: 
Prove the addition and subtraction formulas for sine, cosine, and tangent and use them to solve problems.

Answer: 
Yes. An initial step when solving for x in this problem requires the use of the addition formula for cosine on the left side of the equation.

Example 2:
Problem/activity:
Task
Solve the quadratic equation
$$ x^2 = (2x - 9)^2 $$
using as many different methods as possible.


Concept/skill: 
Understand that the graph of an equation in two variables is the set of all its solutions plotted in the coordinate plane, often forming a curve (which could be a line).

Answer: 
No. This task does not involve an equation in two variables. There is only one variable, x.

Example 3:
Problem/activity:
Task
Suppose $A$ is an angle with vertex $P$, as pictured below:
[IMG]
Draw a circle with center $P$ and with  radius $r \gt 0$.  Explain why the circle
meets each ray of angle $A$ in a single point.  Label these points $Q$ and $R$ respectively.
Draw circles with centers $Q$ and $R$ respectively and radius $r$.  These circles meet at $P$ and a second point to be labelled $B$.
Show that ray $\overrightarrow{PB}$  bisects angle $P$.


Concept/skill: 
Construct a tangent line from a point outside a given circle to the circle.

Answer: 
No. This task does not involve drawing lines that are tangent to circles. The only line that may be drawn is the ray between points P and B.

Now, does the problem or activity shown below enable students to learn the full intent of the following concept or skill?

shot_info: fl_problem_001894_pos_0

HS_0

im_task_000870_neg_0

HS_1

im_task_001160_neg_0

HS_2
standard_description: Given a geometric figure and a rotation, reflection, or translation, draw the transformed figure using, e.g., graph paper, tracing paper, or geometry software. Specify a sequence of transformations that will carry a given figure onto another.
problem_activity: Activity
In this activity students continue to use coordinate transformation notation, but now without the scaffolding of an organizing structure like a table. Students apply transformation rules, then describe the results. One transformation is of a type students have not seen before (the horizontal stretch that is not a dilation).
In the synthesis, students will connect the geometric description of a reflection to the coordinate rule that produces it. They will also draw a conclusion about rules that produce a dilation versus those that produce a stretch in only 1 direction.
Monitor for students who erroneously call the horizontal stretch a dilation. Encourage students to refer to their reference charts for help in attending to precision when describing transformations they’ve learned about.
Making dynamic geometry software available gives students an opportunity to choose appropriate tools strategically (MP5).
Launch
Conversing: MLR2 Collect and Display.
As students work on this activity, listen for and collect the language students use to describe each transformation of quadrilateral
\(ABCD\)
. Write the students’ words and phrases on a visual display. As students review the visual display, ask them to revise and improve how ideas are communicated. For example, a statement such as, “The shape was flipped upside down” can be improved with the statement, “Quadrilateral
\(ABCD\)
was reflected across the
\(x\)
-axis.” This will help students use the mathematical language necessary to precisely describe transformations of figures on the coordinate plane.
Design Principle(s): Optimize output (for explanation); Maximize meta-awareness
Student Facing
[IMG]
Here are some transformation rules. Apply each rule to quadrilateral
\(ABCD\)
and graph the resulting image. Then describe the transformation.
Label this transformation
\(Q\)
:
\((x,y) \rightarrow (2x,y)\)
Label this transformation
\(R\)
:
\((x,y) \rightarrow (x,\text-y)\)
Label this transformation
\(S\)
:
\((x,y) \rightarrow (y,\text-x)\)
Student Response
Teachers with a valid work email address can
click here to register or sign in
for free access to Student Response.
Student Facing
Are you ready for more?
[IMG]
Plot the quadrilateral with vertices
\((4,\text-2),(8,4),(8,\text-6),\)
and
\((\text-6,\text-6)\)
. Label this quadrilateral
\(A\)
.
Plot the quadrilateral with vertices
\((\text-2,4),(4,8),(\text-6,8),\)
and
\((\text-6,\text-6)\)
. Label this quadrilateral
\(A'\)
.
How are the coordinates of quadrilateral
\(A\)
related to the coordinates of quadrilateral
\(A'\)
?
What single transformation takes quadrilateral
\(A\)
to quadrilateral
\(A'\)
?
Student Response
Teachers with a valid work email address can
click here to register or sign in
for free access to Extension Student Response.
Anticipated Misconceptions
If students struggle to keep their work organized, suggest they create a table of inputs and outputs, or create another organizational structure that works for them.
Some students may not be sure how to work with the rule
\((x,y)\rightarrow (y,\text-x)\)
. Ask these students, “What are the coordinates of point
\(A\)
?” (
\((3,\text-4)\)
.) “Which of those is the
\(x\)
-coordinate?” (3.) “In the transformation rule, where does the
\(x\)
land, and what happens to it?” (The
\(x\)
-coordinate lands in the
\(y\)
spot, and it takes on an opposite sign.) Another option is to suggest students write out
\(x=3\)
and
\(y=\text-4\)
, then substitute each value into the transformation rule.
Activity Synthesis
The goal of the discussion is to make connections between the coordinate rules and the geometric descriptions of transformations. Start with these discussion questions:
“In the previous activity, one rule was
\((x,y)\rightarrow (2x,2y)\)
. In this activity, one rule was
\((x,y)\rightarrow (2x,y)\)
. Compare and contrast these rules.” (In the first rule, both coordinates were multiplied by 2. It is stretched both vertically and horizontally by the same factor. The second rule just had the
\(x\)
-coordinate multiplied by 2. It was only stretched in one direction.)
“Can we call
\((x,y)\rightarrow (2x,y)\)
a dilation? Why or why not?” (No. In a dilation, the figure is stretched in all directions by the same factor, not just 1 direction. Also, in this example we can see that the angles of the dilated figure are not congruent to the angles in the original.)
“Can we call
\((x,y)\rightarrow (2x,y)\)
a translation? Why or why not?” (No. A translation is a rigid motion—it produces a result that does not change size or shape.)
Now ask students, “The rule
\((x,y) \rightarrow (x, \text-y)\)
is a reflection across the
\(x\)
-axis. Look at the definition of a reflection on your reference chart. Why does this rule produce a reflection?” Guide students through the different aspects of the geometric definition of a reflection. Consider displaying an image of the solution and drawing segments that connect pairs of original and image points. Important ideas that should surface are:
The
\(y\)
-coordinates of the original and image points have the same absolute value, so the distance from the
\(x\)
-axis is the same for each.
The sign of the image’s
\(y\)
-coordinate is opposite the original, so the image is on the opposite sign of the axis as the original.
Connecting the image and original points, we get a vertical line because the
\(x\)
-coordinates are the same. So this segment is perpendicular to the line of reflection, or the
\(x\)
-axis.


aligns: yes