Lesson 8Reasoning About Solving Equations (Part 2)
Learning Goal
Let’s use hangers to understand two different ways of solving equations with parentheses.
Learning Targets
I can explain how a balanced hanger and an equation represent the same situation.
I can explain why some balanced hangers can be described by two different equations, one with parentheses and one without.
I can find an unknown weight on a hanger diagram and solve an equation that represents the diagram.
I can write an equation that describes the weights on a balanced hanger.
Warm Up: Equivalent to
Problem 1
Select all the expressions equivalent to
Activity 1: Either Or
Problem 1
Explain why either of these equations could represent this hanger:
Find the weight of one circle. Be prepared to explain your reasoning.
Activity 2: Use Hangers to Understand Equation Solving, Again
Problem 1
Here are some balanced hangers. Each piece is labeled with its weight.
Assign one of these equations to each hanger:
Hanger A:
Hanger B:
Hanger C:
Hanger D:
Hanger A
Hanger B
Hanger C
Hanger D
For each diagram, explain how to figure out the weight of a piece labeled with a letter by reasoning about the diagram.
For each diagram, explain how to figure out the weight of a piece labeled with a letter by reasoning about the equation.
Lesson Summary
The balanced hanger shows 3 equal, unknown weights and 3 2-unit weights on the left and an 18-unit weight on the right.
There are 3 unknown weights plus 6 units of weight on the left. We could represent this balanced hanger with an equation and solve the equation the same way we did before.
Since there are 3 groups of
The two sides of the hanger balance with these weights: 3 groups of
The two sides of the hanger will balance with
We can remove 2 units of weight from each side, and the hanger will stay balanced. This is the same as subtracting 2 from each side of the equation.
An equation for the new balanced hanger is
Here is a concise way to write the steps above: