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I'm really having trouble trying to figure out a function.

So, the surface area $S$ of a sphere is a function of its radius $r$ given by $S(r) = 4\pi r^2$. I'm trying to find $S(2)$ and $S(3)$.

Am I supposed to plug in $2$ and $3$ respectively for $r$? Silly question perhaps, but I'm confused. :(

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    Yes, that’s exactly what you’re supposed to do.2012-09-18

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$S(r)=4\pi r^2$ $S(t)=4\pi t^2$ $S(\text{bananas})=4\pi (\text{bananas})^2$ $S(2)=4\pi(2)^2$ $S(3)=4\pi(3)^2$

Keep in mind you can't actually square literal bananas, but you could call a variable "bananas" and this would work. $S$ represents what we do to the input, regardless of what the input is.

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Yes. "r" is nothing more than an independent variable. In this case, it represents the radius of your sphere. For your purposes, think of a function as a machine that has both input and output. If you are looking for the surface area of a sphere with radius r, then "feed" r into your function, S, and out pops the surface area. This works for all r > 0.

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    Works for $r=0$, too. :-)2012-09-18