Hi,

I am solving a problem which involves calculating the surface are of a solid revolution about the x – axis. I have found that the surface area can be given by:

I have done this using the trapezium rule as I know the values of r and d, so I have a rough estimate of a figure I am aiming for.

The question I am trying to answer says to use the standard integral:

I am struggling to interpret the r+rd/√(r^2-x^2) into the form dx/√(k^2-x^2) in order to evaluate the integral. Any help or guidance would be appreciated as I have spent too much time trying to do this.

Thanks