Geometry Net

Unit 2 Geometry Review Day 2

Good for you! You are taking care of business.

You need scratch paper, pencil, and a calculator!

Poll

What do you already know about surface area?

• It is sometimes abbreviated as SA

• It is the area of the faces of a 3-D figure

• It can be kind of a pain in the neck

• It is the like covering a 3-D shape, like wrapping a package.

• It is measured in units²

Poll

Do you know what a net is?

• Of course. I use it when I go fishing.

• No.

• Yes, it shows the 3-D object in 2-D.

• Yes, it is like the object if you took it apart and laid it flat.

• I could really use a refresher here.

A Net shows the faces of a 3-D figure.

• Watch this 3 minute video of me showing you the 3 nets that are on your test.

Multiple Choice

Which prism's net has 6 congruent squares?

• Rectangular Prism

• Hexagonal Prism

• Cube

• Triangular Prism

Multiple Choice

This is the net for which figure?

• Rectangular Prism

• Hexagonal Pyramid

• Hexagonal Prism

• Rectangular Pyramid

Multiple Choice

Which is the net of a square pyramid?

Multiple Choice

Which net has 4 triangles as its lateral faces?

Finding the surface area?

Look at the shapes that make up the figure. Draw nets.

Find the area of each shape then add them together.

Know what LATERAL AREA is.

Lateral Area of a Cone

You have to know how to find the lateral area of the cone, not the surface area. In this picture, it is the green part. Use

 $\pi\times r\times l$  

Multiple Choice

Find the lateral area of a cone with radius 3cm and slant height 7cm.

$$LA=\pi rl$$  

• 94.2 cm²

• 65.94 cm²

• 3.14 cm²

Surface Area of a Sphere

Use the formula

 $SA=4\pi r^2$  
ex. Find the surface area of a sphere with radius 6.
 $SA=4\times3.14\times6^2$  
 $SA=4\times3.14\times36$   (exponents first)
 $SA=452.16\approx452\ units^2$  

Multiple Choice

Find the surface area of a sphere with radius 5 in. Use the formula

$$SA=4\pi r^2$$  

• 125.6 square inches

• 56.25 square inches

• 314 square inches

Find the surface area of a triangular prism

I'm not going to lie...these are a real pain. Watch this 3 min 52 second video. You have to show work for this kind on your test.

Poll

What is the formula for area of a triangle? Just checking; the bases of triangular prisms are triangles, so...

• $$A=lw$$

• $$A=bh$$

• $$A=bh\div2$$

Multiple Choice

Ok! Now let's find the surface area of this triangular prism.

• 108 units²

• 96 units²

• 420 units²

Multiple Choice

Find the surface area of a cylinder with diameter 20 inches and height 15 inches. Use the formula

$$SA=2\pi r^2+2\pi rh$$  

• Easy! That's  $$2\times3.14\times20^2+2\times3.14\times20\times15$$  

• Wait! Trick question. If the diameter is 20, that means r=10, so that's  $$2\times3.14\times10^2+2\times3.14\times10\times15$$  

Multiple Choice

Find the surface area of a cylinder with a height of 8 cm and a diameter of 10 cm.

$$2\pi r^2+2\pi rh$$  

• 80 cm² Don't pick this one. You're just multiplying the numbers. You have to use the formula!!

• 226.08 square cm

• 408.2 square cm

Multiple Choice

Which shows a horizontal cross section?

Multiple Choice

What shape would a vertical cross section of this cylinder be?

• Circle

• Square

• Rectangle

• Triangle

Use Proportions to solve.

 $\frac{Purple\ height\ }{Purple\ base}=\frac{Green\ height}{Green\ base}$  
 $\frac{f}{15}=\frac{24}{20}$   Cross multiply to solve

 $20f=15\left(24\right)$  
 $20f=360$  
 $f=18mm$  

Multiple Choice

Your turn! Don't guess. Set up a proportion (2 fractions equal to each other)

• 10 ft

• 11 ft

• 12 ft

• 15 ft

For stuff we didn't cover, please use the corrections form!

I know I didn't cover every type of problem here. I will grade your quizizz tomorrow. Check your Unit 2 Test feedback to see which questions you haven't earned back points on yet and use the form :)