Page 119 - TB_5B

Activity 1 Surface Area of Rectangular Prisms

The sum of all the areas of the faces of a solid figure 5 cm

is called the surface area. Find the surface area of a
prism that is 3 cm by 2 cm by 5 cm.

3 cm 2 cm

Method 1 Use the sum of the areas of faces.

Label all the faces and then find the area of each face.

Then add up the areas.

Face Area(cm2)
AA A 15
10
B 6
10
B CDE C 6
B CDE D 15

FF E
F

Surface area A B C D E F 15 10 6 10 6 15 62 (cm2)

Method 2 Use the areas of faces that are opposite to each other.

Each pair of opposite faces, A and F, B and D, and C and E, are congruent.
Find the area of 1 face from each pair and multiply it by 2.

Face Area(cm2) Surface area A B C) 2
A 15 15 10 6) 2
B 10 62 (cm2)
C 6

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