Hello! I want to calculate an integral of the form [tex] \int d \vec k f(\vec k \cdot \vec x) g(k^2) \vec k, [/tex] where k and x are 3-dimensional vectors and integration spans the whole 3D volume. I wonder what is the general approach to the problem? Were it not for the vector k term in the integral, one could just switch to the spherical coordinates and perform integration over two variables (|k| and one of the angles, while the other angle gives just a constant factor). But now it is not clear how to do that, since the result of the integration is supposed to be a 3-vector itself. Any suggestions or references are welcome.