#### Circular Cross-Section

For a circular cross-section of radius , Eq.(B.11) tells us that the squared radius of gyration about any line passing through the center of the cross-section is given by

Using the elementrary trig identity , we readily derive

For a circular *tube* in which the mass of the cross-section lies
within a circular *annulus* having inner radius and outer
radius , the radius of gyration is given by

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Rectangular Cross-Section