12.3b Surface Area of Pyramids and Cones

State Standards8, 9: Solve problems involving

the surface area lateral area of geometric solids and COMMIT TO MEMORY THE NECESSARY FORMULAS.

Lesson Goals• Find the surface area of a

cone.

definitions• Cone

– Base: a circle– Lateral surface: a sector of a circle– Altitude: the perpendicular distance between the vertex

and the base.

slant heightaltitude

theorem

Surface Area of a Cone

represents the radius of the circle.r

You tryFind the surface area.

12 ft

5 ft

13 ft

2SA r r

25 5 13SA

25 65SA 22 282.6 ft90 ftSA

2 2 25 12 2 169

13

Example2SA r r

26.7 6.7 12.2SA

44.89 81.74SA

22 397.82 ft126.63 ftSA

2 2 26.7 10.2 2 44.89 104.04

2 148.93 12.2

Find the missing measurements of the right cone.

2SA r r

219.9 25 5

219.9 25 5

70 25 5

45 5

9 in

Find the missing measurements of the right cone.

Today’s Assignmentp. 738: 20 – 25, 27, 36, 44 – 46