Cogito
Geometry · Chapter 8 · Lesson 2
Surface Area
Unfold it and add up the faces.
11 problems · about 22 minutes · G-GMD.A.3, G-MG.A.1
What this lesson teaches
The student computes surface area from a net.
- A net is the solid unfolded, and its area is the surface area.
- Add every face — a cuboid has three matching pairs.
- Surface area is in square units; volume is in cubic units.
Warm Up
Straightforward practice. Get the method working first.
4 problemsCube with edge 4. Surface area?
Answer 96
Why 96.
Cube with edge 2. Surface area?
Answer 24
Why Six faces of 4.
Cube with edge 5. Surface area?
Answer 150
Why Six faces of 25.
Cuboid 2 by 3 by 4. Surface area?
Answer 52
Why 12 + 16 + 24, doubled halves.
Build It Up
The same ideas with more to keep track of.
3 problemsCube with edge 2. Volume?
Answer 8
Why 2 × 2 × 2.
Are surface area units squared or cubed? 1 for squared, 2 for cubed.
Answer 1
Why It covers a surface.
How many faces does a triangular prism have?
Answer 5
Why Two triangles, three rectangles.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
4 problemsA cylinder net has how many circles?
Answer 2
Why Top and bottom.
Sort each quantity by its units.
Answer Square units: Surface area · Cubic units: Volume · Plain units: Edge length
Why Count the dimensions each one uses.
The Cube: A cube with edge 3. What is its surface area?
Answer 54
Why 54.
The Faces: How many faces does a cuboid have?
Answer 6
Why 6.