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# Estimating Surface Area PowerPoint PPT Presentation

Estimating Surface Area. The art of math…. You can’t always get an exact answer when looking for the surface area of a complex 3-D shape We use estimation methods to get an approximate answer We will demonstrate this with a cone (even though there is a formula available).

Estimating Surface Area

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## Estimating Surface Area

The art of math…

You can’t always get an exact answer when looking for the surface area of a complex 3-D shape

We use estimation methods to get an approximate answer

We will demonstrate this with a cone (even though there is a formula available)

Cone

### Model Your Shape

• Simple shapes can be used to estimate the surface area of more complicated 3-D objects

• What shape do you think we should use?

This will provide an estimate by using a shape we are more familiar with

If we only use the sides of the cylinder will this is an over or under estimate?

### Estimating with cylinders

You can see from the “net” that the cone had more surface area than the cylinders

What happens to our estimate if we use larger Cylinders?

### It was an underestimate

The cylinders are obviously larger than the cone

Do you think this is more accurate? How do you know?

### Over Estimating

What if we averaged our results? Or tried cylinders a little smaller than these but bigger than the first set?

What else could we try?

### Over Estimating

This is still an underestimate, BUT it is a better model for the cone

This gives a much closer estimate than our first approach

### What happens if you increase the number of cylinders?

There is a formula for surface area of a cone

Is there a formula for this shape?

What shape should we use to calculate the surface area of this one?

### More complicated shapes

• What do you think we should do?

### This looks pretty good…

• Don’t forget, not all the surface area of the boxes needs to be counted.