How to determine the surface area of cylinder? (conversation between Teacher and student)

T: Today we will learn about the surface area of cylinder. Before we learn about the surface area of cylinder, do you remember how to determine the surface area of cube? Who want to share?
S: Yes I want to try Sir. The surface area of cube is 6 x S2
T: Oh good Adam. I have a box here. Is anybody wanted to share how to determine the surface area this box without formula?
S: I am Sir! The surface area of this box is the sum of all sides’ /faces’ area of the cube. (Student show up the surface area of the box)
T: Wow great Lisa. And now, I have a can. What do you think when you see this can?
S: It’s represent of cylinder Sir.
T: Do you have any example of cylinder around of us?
S: So many cans made like a cylinder, daily tools and so on.
T: Oh good, it is true. Next, if I want to know the surface area of this can without formula. What step that you can do?
S: Hemm..  I don’t know Sir.
T: Oh.. You can use the same manner like as the cube.
S : Yes Sir. The surface area of this can is all the surface of these bodies/sides/faces. (Student show the surface of the can)
T: oh great.. Now, I have a piece of paper. Can you covering the body of this can with this paper?
S: (covering the body of can by using paper)
T: Can you give signs the paper that covered the body of can? Let do it!
S: (student gives signs)
T: Any other faces of can that not yet covering?
S: Yes, the top and the bottom.
T: Ok, let covering and give sign same as the body.
S: (the student covering and giving signs)
T: After you signed the paper, I have scissor that you can use to cut. What do you think?
S: Ok, I will cut the paper based on the signed that I have. (Student cut the paper)
T: Ok what do you get from this activity?
S: From this activity I get the models of rectangle and 2 circles. I think these rectangle and 2 circles represent the surface area of a can. To know the surface area of cylinder or can, we can sum of the area of this models. It is the sum of area of rectangle and two circles.
T: Do you remember the formula of area rectangle and 2 circles? Come forward to show it!
S: (student come in front of class and write the formulas of area the rectangle and two circles)
T: So, how to find the surface area of cylinder from the formula that have you write?
S: The surface area of cylinder is (p x l) + (2 x pi x r x r)
T: Great, you have determine the surface area of cylinder. What l is mean?
S: l mean the perimeter of the circle. it is 2 pi r.
T: Ok, goo. And based on the activity, we can make more simple the surface area of cylinder right?
S: Yups Sir, the the surface area of cylinder become 2.pi.r.r + 2.pi.r.h And we can make more simple become 2.pi.r(r+h).


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