Posted by **Nancy** on Monday, November 8, 2010 at 11:16pm.

Express the amount of material needed to make a can as a function of the radius. In other words, find a function A(r) such that A represents the surface area (in square inches) of the cylinder and r is the radius (in inches).

my answer (not sure)

A(r) = r^2 + 2r + 29 ?

- algebra -
**Reiny**, Monday, November 8, 2010 at 11:27pm
This looks like a continuation of your last problem

Visualize taking a tin can apart.

you would have 2 circles, the top and the bottom

plus the sleeve that forms the can.

Pretend you are opening it up by cutting along the height of the can.

Would you not have a rectangle whose length is the circumference of the circle, and whose width is the height ?

So the total area would be

top + bottom + rectangle

= πr^2 + πr^2 + (2πr)h, where h is the height.

= 2πr^2 + (2πr)h

This is precisely what I used in the previous question.

You will need the height, or else be able to calculate it like in your previous question when the volume was given.

- algebra -
**Nancy**, Monday, November 8, 2010 at 11:43pm
Thank you!!

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