Mr. Liu: (Mr. Liu drew two figures

Mr. Liu: (Mr. Liu drew two figures on the blackboard. The top one was a rectangle and the bottom one a square. He
pointed to the blackboard and asked his students). What is the figure on the top called?
S 1: A rectangle.
Mr. Liu: What about the bottom one?
S2: A square.
Mr. Liu: What is the perimeter of a rectangle? What is the perimeter of a square? Who is willing to come to the front
and explain to us? (He saw many hands and pointed to S3). O.K., S3?
S3: (Pointed at the rectangle) The perimeter of a rectangle is the surrounding edges.
Mr. Liu: Please be more precise.
S3: The perimeter of a rectangle is the length of the four sides.
Mr. Liu: That’s right. What about a square?
S4: The perimeter of a square is also the length of the four sides.
Mr. Liu: So, how is the perimeter of a rectangle related to the length and width of the rectangle?
S5: The perimeter of a rectangle is two times the sum of the length and width of the rectangle.
Mr. Liu: That means that we can represent the perimeter of a rectangle using two times the sum of the length and
width. What about a square?
S6: The perimeter of a square is four times the length of a side.
Mr. Liu: So how can we represent the relationship between the perimeter of a square and its sides?
S7: Just multiple a side by 4.
Mr. Liu: How can we use letters to represent the perimeter of a rectangle?
S8: The sum of the length and the width multiplied by 2.
Mr. Liu: Think about it. How can we use letters to represent this?
S1: Equals to the quantity a plus b times 2.
Mr. Liu: What about the formula for a square?
S2: 4a.
Mr. Liu: If the length of a rectangle is 4 cm and the width is 3 cm. What is the perimeter?
S4: The perimeter of the rectangle is 14 cm.
Mr. Liu: What is it? Provide the process.
S4: Equals to the quantity 3 plus 4 times 2.
Mr. Liu: Can we say the quantity 3 plus 4 times 2? What is the result?
Group: 14.
Mr. Liu: What about the perimeter of a square with a side equal to 3 cm?
S8: 4 × 3 = 12 cm.