1. Warm Up
Find the missing side length of each right triangle with legs a and b and hypotenuse c.
1. a = 7, b = 24
2. c = 15, a = 9
3. b = 40, c = 41
4. a = 5, b = 5
5. a = 4, c = 8
c = 25
b = 12
a = 9

2. Objectives
Learn and apply the formula for the surface area of a pyramid.
Learn and apply the formula for the surface area of a cone.

3. The vertex of a pyramid is the point opposite the base of the pyramid
The vertex of a pyramid is the point opposite the base of the pyramid. The base of a regular pyramid is a regular polygon, and the lateral faces are congruent isosceles triangles. The slant height of a regular pyramid is the distance from the vertex to the midpoint of an edge of the base. The altitude of a pyramid is the perpendicular segment from the vertex to the plane of the base.

4. The lateral faces of a regular pyramid can be arranged to cover half of a rectangle with a height equal to the slant height of the pyramid. The width of the rectangle is equal to the base perimeter of the pyramid.

6. Example 1A: Finding Lateral Area and Surface Area of Pyramids
Find the lateral area and surface area of a regular square pyramid with base edge length 14 cm and slant height 25 cm. Round to the nearest tenth, if necessary.
Lateral area of a regular pyramid
P = 4(14) = 56 cm
Surface area of a regular pyramid
B = 142 = 196 cm2

7. Example 1B: Finding Lateral Area and Surface Area of Pyramids
Find the lateral area and surface area of the regular pyramid.
Step 1 Find the base perimeter and apothem.
The base perimeter is 6(10) = 60 in.
The apothem is , so the base area is

8. Check It Out! Example 1
Find the lateral area and surface area of a regular triangular pyramid with base edge length 6 ft and slant height 10 ft.
Step 1 Find the base perimeter and apothem. The base perimeter is 3(6) = 18 ft.
The apothem is so the base area is

9. The vertex of a cone is the point opposite the base
The vertex of a cone is the point opposite the base. The axis of a cone is the segment with endpoints at the vertex and the center of the base. The axis of a right cone is perpendicular to the base. The axis of an oblique cone is not perpendicular to the base.

10. The slant height of a right cone is the distance from the vertex of a right cone to a point on the edge of the base. The altitude of a cone is a perpendicular
segment from the vertex of the cone to the plane of the base.

11. Example 2A: Finding Lateral Area and Surface Area of Right Cones
Find the lateral area and surface area of a right cone with radius 9 cm and slant height 5 cm.
L = rℓ
Lateral area of a cone
= (9)(5) = 45 cm2
Substitute 9 for r and 5 for ℓ.
S = rℓ + r2
Surface area of a cone
= 45 + (9)2 = 126 cm2
Substitute 5 for ℓ and 9 for r.

12. Example 2B: Finding Lateral Area and Surface Area of Right Cones
Find the lateral area and surface area of the cone.
Use the Pythagorean Theorem to find ℓ.
L = rℓ
Lateral area of a right cone
= (8)(17)
= 136 in2
Substitute 8 for r and 17 for ℓ.
S = rℓ + r2
Surface area of a cone
= 136 + (8)2
= 200 in2
Substitute 8 for r and 17 for ℓ.

13. Check It Out! Example 2
Find the lateral area and surface area of the right cone.
Use the Pythagorean Theorem to find ℓ. ℓ
L = rℓ
Lateral area of a right cone
= (8)(10)
= 80 cm2
Substitute 8 for r and 10 for ℓ.
S = rℓ + r2
Surface area of a cone
= 80 + (8)2
= 144 cm2
Substitute 8 for r and 10 for ℓ.

14. Example 3: Exploring Effects of Changing Dimensions
The base edge length and slant height of the regular hexagonal pyramid are both divided by 5. Describe the effect on the surface area.

15. base edge length and slant height divided by 5: original dimensions:
Example 3 Continued
base edge length and slant height divided by 5:
original dimensions:
Notice that If the base edge length and slant height are divided by 5, the surface area is divided by 52, or 25.

16. Check It Out! Example 3
The base edge length and slant height of the regular square pyramid are both multiplied by . Describe the effect on the surface area.

17. Check It Out! Example 3 Continued
8 ft
10 ft
8 ft
original dimensions:
multiplied by two-thirds:
S = Pℓ + B 12
S = Pℓ + B 12
= 585 cm2
= 260 cm2
By multiplying the dimensions by two-thirds, the surface area was multiplied by .

18. Example 4: Finding Surface Area of Composite Three-Dimensional Figures
Find the surface area of the composite figure.
Left-hand cone:
The lateral area of the cone is
L = rl = (6)(12) = 72 in2.
Right-hand cone:
Using the Pythagorean Theorem, l = 10 in.
The lateral area of the cone is
L = rl = (6)(10) = 60 in2.

19. Check It Out! Example 4
Find the surface area of the composite figure.
Surface Area of Cube without the top side:
S = 4wh + B
S = 4(2)(2) + (2)(2) = 20 yd2

20. Example 5: Manufacturing Application
If the pattern shown is used to make a paper cup, what is the diameter of the cup?
The radius of the large circle used to create the pattern is the slant height of the cone.
The area of the pattern is the lateral area of the cone. The area of the pattern is also of the area of the large circle, so

21. Example 5 Continued
If the pattern shown is used to make a paper cup, what is the diameter of the cup?
Substitute 4 for ℓ, the slant height of the cone and the radius of the large circle.
r = 2 in.
Solve for r.
The diameter of the cone is 2(2) = 4 in.

22. Check It Out! Example 5
What if…? If the radius of the large circle were 12 in., what would be the radius of the cone?
The radius of the large circle used to create the pattern is the slant height of the cone.
The area of the pattern is the lateral area of the
cone. The area of the pattern is also of the area of
the large circle, so

23. Check It Out! Example 5 Continued
What if…? If the radius of the large circle were 12 in., what would be the radius of the cone?
Substitute 12 for ℓ, the slant height of the cone and the radius of the large circle.
r = 9 in.
Solve for r.
The radius of the cone is 9 in.