<p>By a unit cylinder <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\cal{C}}_{1}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <msub> <mrow> <mrow> <mi mathvariant="script">C</mi> </mrow> </mrow> <mrow> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> we mean the right-circular cylinder of radius one and height one. It is a convex solid (that is, a line segment joining any two points in <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({\cal{C}}_{1}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <msub> <mrow> <mrow> <mi mathvariant="script">C</mi> </mrow> </mrow> <mrow> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> lies entirely in <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\({\cal{C}}_{1}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <msub> <mrow> <mrow> <mi mathvariant="script">C</mi> </mrow> </mrow> <mrow> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation>), with volume <i>π</i> and surface area 4<i>π</i>. Thus, in relation to a unit sphere, <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\({\cal{C}}_{1}\)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <msub> <mrow> <mrow> <mi mathvariant="script">C</mi> </mrow> </mrow> <mrow> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> has the same surface area but only three-fourths the volume.</p>
By a unit cylinder \({\cal{C}}_{1}\) we mean the right-circular cylinder of radius one and height one. It is a convex solid (that is, a line segment joining any two points in \({\cal{C}}_{1}\) lies entirely in \({\cal{C}}_{1}\)), with volume π and surface area 4π. Thus, in relation to a unit sphere, \({\cal{C}}_{1}\) has the same surface area but only three-fourths the volume.