few_shots: 
Example 1:
Concept/skill: 
Prove the addition and subtraction formulas for sine, cosine, and tangent and use them to solve problems.

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


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:
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).

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


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

Example 3:
Concept/skill: 
Construct a tangent line from a point outside a given circle to the circle.

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 $P$.


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, determine whether the following problem or activity can enable students to understand the concepts or skills in the provided description.

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: Apply the properties of operations to generate equivalent expressions. For example, apply the distributive property to the expression 3 (2 + x) to produce the equivalent expression 6 + 3x; apply the distributive property to the expression 24x + 18y to produce the equivalent expression 6 (4x + 3y); apply properties of operations to y + y + y to produce the equivalent expression 3y.
problem_activity: Activity
The purpose of this activity is for students to interact with contexts in which the direction of inequality is the opposite of what they might expect if they try to solve like they would with an equation. For example, in the second problem, the original inequality is
\(9(7-x) \leq 36\)
, but the solution to the inequality is
\(x \geq 3\)
.
Some students might solve the associated equation and then test values
of
\(x\)
to determine the direction of inequality. That method will be introduced in more generality in the next lesson. This activity emphasizes thinking about the context in deciding the direction of inequality.
Launch
Keep students in the same groups. Give 5–10 minutes of quiet work time and partner discussion followed by a whole-class discussion.
Student Facing
Kiran has
$
100 saved in a bank account. (The account doesn’t earn interest.) He asked Clare to help him figure out how much he could take out each month if he needs to have at least
$
25 in the account a year from now.
Clare wrote the inequality
\(\text-12x + 100 \geq 25\)
, where
\(x\)
represents the amount Kiran takes out each month. What does
\(\text-12x\)
represent?
Find some values of
\(x\)
that would work for Kiran.
We could express
all
the values that would work using either
\(x \leq \text{__ or } x \geq \text{__}\)
. Which one should we use?
Write the answer to Kiran’s question using mathematical notation.
A teacher wants to buy 9 boxes of granola bars for a school trip. Each box usually costs
$
7, but many grocery stores are having a sale on granola bars this week. Different stores are selling boxes of granola bars at different discounts.
If
\(x\)
represents the dollar amount of the discount, then the amount the teacher will pay can be expressed as
\(9(7-x)\)
. In this expression, what does the quantity
\(7-x\)
represent?
The teacher has
$
36 to spend on the granola bars. The equation
\(9(7-x)=36\)
represents a situation where she spends all
$
36. Solve this equation.
What does the solution mean in this situation?
The teacher does not have to spend all
$
36. Write an inequality relating 36 and
\(9(7-x)\)
representing this situation.
The solution to this inequality must either look like
\(x \geq 3\ \text{or } x \leq 3\)
. Which do you think it is? Explain your reasoning.
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?
Jada and Diego baked a large batch of cookies.
They selected
\(\frac14\)
of the cookies to give to their teachers.
Next, they threw away one burnt cookie.
They delivered
\(\frac25\)
of the remaining cookies to a local nursing home.
Next, they gave 3 cookies to some neighborhood kids.
They wrapped up
\(\frac23\)
of the remaining cookies to save for their friends.
After all this, they had 15 cookies left. How many cookies did they bake?
Student Response
Teachers with a valid work email address can
click here to register or sign in
for free access to Extension Student Response.
Activity Synthesis
The purpose of the discussion is to let students voice their reasoning about the direction of the inequality by reasoning about the context. Ask students to share their reasons for choosing the direction of inequality in their solutions. Some students may notice that the algebra in both problems involves multiplying or dividing by a negative number. Honor this observation, but again, the goal is not to turn this observation into a rule for students to memorize and follow. Interpreting the meaning of the solution in the context should remain at the forefront.
As students model real-world situations, questions about the interpretation of the mathematical solution should continue to come up in the conversation. For instance, the amount of the granola bar discount cannot be
$
3.5923, even though this is a solution to the inequality
\(x \geq 3\)
. The value -10 is a solution to Kiran’s inequality, even though he can’t withdraw -10 dollars. Students can argue that negative values for
\(x\)
simply don’t make sense in this context. Some may argue that we should interpret
\(x=\text-10\)
to mean that Kiran deposits
$
10 every month.
Engagement: Develop Effort and Persistence
. Break the class into small discussion groups and then invite a representative from each group to report back to the whole class.
Supports accessibility for: Language; Social-emotional skills; Attention
Representing, Writing, Conversing: MLR8 Discussion Supports.
Use this routine to support whole-class discussion. After a student shares their reasons for the direction of the inequality in their solution, ask students to restate and/or revoice what they heard using mathematical language. Consider providing students time to restate what they hear to a partner, before selecting one or two students to share with the class. Ask the original speaker if their peer was accurately able to restate their thinking. This will help students understand how context determines the direction of inequality.
Design Principle(s): Support sense-making


aligns: no