Let $\overline{a}$ and $\overline{b}$ be non-collinear vectors. If the vectors $(\mathrm{\lambda }-1)\overline{\mathrm{a}}+2\overline{\mathrm{b} }\text{and }3\overline{\mathrm{a}}+\mathrm{\lambda }\overline{\mathrm{b}}$ are collinear,  then the set of all possible values of $\lambda$ is