True. When c<0, all the coefficients of the variables become positive as in x^2/A^2+y^2/B^2+z^2/C^2=1, the standard equation of an ellipsoid, where a=1/A^2, b=1/B^2 and c=-1/C^2. The ellipsoid has the origin as its centre. A, B and C are the lengths of the semi-axes or the radii of the ellipsoid.