Surface area of frustum

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nickyp

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Oct 22, 2010
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I have been trying to figure this out for hours. I can't seem to find where this formula comes from.

-Prove that the surface area of a frustum is SA = 2(pi)rL ; where r = (r1 + r2)/2

any help is appreciated.

I tried to take the formular for surface area of a cone and subtract the smaller cone from the larger cone but I havent been able to end with the formula 2(pi)rL

thanks
 
That cone subtraction might help, but are we talking about the LATERAL surface area or ALL of the surface area?
 
You're going to have to show what it is you are doing. The fact taht you failed to mnention the tio of the frustrum concerns me.

"I think just the lateral surface area, ..."

I began to beleive that is was just the lateral surface area.

"... not the end of the cone."

Now, I'm not sure, again.

Beings as this is a calculus class, have you noticed that a cone is a simple revolution of a line segment? You may wish to consier the line \(\displaystyle \frac{x}{r} + \frac{y}{h}=1\).
 
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