# area of surface of revolution

The general surface of revolution is obtained when the arc is rotated about an arbitrary axis. If one chooses Cartesian coordinates  , and specializes to the case of a surface of revolution generated by rotating about the $x$-axis a curve described by $y$ in the interval   $[a,b]$, its area can be calculated by the formula

 $A=2\pi\int_{a}^{b}y\,\sqrt{1+\left(\frac{dy}{dx}\right)^{2}}\,dx$

Similarly, if the curve is rotated about the $y$-axis rather than the $x$-axis, one has the following formula:

 $A=2\pi\int_{a}^{b}x\,\sqrt{1+\left(\frac{dx}{dy}\right)^{2}}\,dy$

The general formula is most often seen with parametric coordinates. If $x(t)$ and $y(t)$ describe the curve, and $x(t)$ is always positive or zero, then the area of the general surface of revolution $A$ in the interval $[a,b]$ can be calulated by the formula

 $A=2\pi\int_{a}^{b}y\,\sqrt{\left(\frac{dx}{dt}\right)^{2}+\left(\frac{dy}{dt}% \right)^{2}}\,dt$

To obtain a specific surface of revolution, translation  or rotation can be used to move an arc before revolving it around an axis. For example, the specific surface of revolution around the line $y=s$ can be found by replacing $y$ with $y\!-\!s$, moving the arc towards the $x$-axis so  $y=s$  lies on it. Now, the surface of revolution can be found using one of the formulae above.

In this specific case, replacing $y$ with  $y=s$,  the area of a surface of revolution is found using the formula

 $A=2\pi\int_{a}^{b}(y-s)\sqrt{\left(\frac{dy}{dx}\right)^{2}}\,dy$
Title area of surface of revolution AreaOfSurfaceOfRevolution 2014-07-24 18:36:37 2014-07-24 18:36:37 rspuzio (6075) pahio (2872) 13 rspuzio (2872) Topic msc 53A05 msc 26B15 area of revolution surface area of revolution SurfaceOfRevolution2 VolumeOfSolidOfRevolution