<PRE><B>Question 1128411</B>
&lt;br&gt;
Thank you, but I&#39;ll use r for the radius instead of x; that&#39;s less confusing.  I can call it x when I put the function in my calculator, since my calculator doesn&#39;t recognize the &quot;r&quot;.&lt;br&gt;
The cost is 4 cents per square inch for the top and bottom and 1 cent per square inch for the sides:&lt;br&gt;
{{{C(r) = 4(2(pi)r^2)+1(2(pi)rh)}}}&lt;br&gt;
We need the function in terms of a single variable.  To do that, we use the given volume and the formula for the volume to find the height h in terms of r:&lt;br&gt;
{{{45 = (pi)r^2h}}}
{{{h = 45/((pi)r^2)}}}&lt;br&gt;
Now our cost function is in terms of r only:&lt;br&gt;
{{{C(r) = 8(pi)r^2+2(pi)r((45)/((pi)r^2)) = 8(pi)r^2+90/r}}}&lt;br&gt;
Put that equation in your graphing calculator, graph it, and find the value of x (r) that gives the minimum function value (minimum cost).&lt;br&gt;
Your graph should look something like this:
{{{graph(400,400,-1,5,-50,400,8(pi)x^2+90/x)}}}</PRE>