1. The problem statement, all variables and given/known data In spherical polar coordinates, a vector F is given by F=(r*costheta*cosphi)rhat + (r*costheta*sinphi)thetahat + (r*sintheta*cosphi)phihat Check the validity of the divergence theorem for this vector and the volume that is one octant of a sphere radius b. 2. Relevant equations [tex]\oint[/tex]F [tex]\cdot[/tex] dA = [tex]\int[/tex]Vgrad[tex]\cdot[/tex]Fd3r 3. The attempt at a solutionThe solution for this problem is in my book, and I am having difficulty following it, I think because it is in polar coordinates, and I am still trying to get used to them. The author proceeds to divide the surface into four area elements: spherical surface : dA = rhat(b^2)*sintheta*dtheta*dphi before I go on to any of the other elements, could someone please help me understand how the author derived this expression? Thanks.