%
% Computes (the volume of the solid obtained by slicing the torus 
% parallel to the x-axis at t and -t) - 20.
%
% It's necessary to do this to use the function with Matlab's fzero 
% function (which assumes equations are set up in standard form: 
% f(x) = 0).
%
function getToZero = volDiskLess20(t)
getToZero = volumeDisk(t) - 20;