standard_description: Prove polynomial identities and use them to describe numerical relationships. For example, the polynomial identity (x^(2) + y^(2))^(2) = (x^(2 )– y^(2))^(2) + (2xy)^(2 )can be used to generate Pythagorean triples.
problem_activity: Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for multiplying a one-digit number and a two-digit number, which will be helpful later in this lesson when students continue to practice multiplying within 100.
Launch
Display one expression.
“Give me a signal when you have an answer and can explain how you got it.”
1 minute: quiet think time
Activity
Record answers and strategy.
Keep expressions and work displayed.
Repeat with each expression.
Student Facing
Find the value of each expression mentally.
\(4\times10\)
\(4\times20\)
\(4\times21\)
\(4\times24\)
Student Response
Teachers with a valid work email address can
click here to register or sign in
for free access to Student Response.
Activity Synthesis
“How did you figure out the more challenging products?” (Once I knew
\(4\times20\)
, I was able to build on it to find
\(4\times21\)
and
\(4\times24\)
by just adding more fours. I knew that 4 groups of 25 make 100, so I took away 4 to find 4 groups of 24.)


aligns: no