If  $\overline{\mathrm{a}}=3\widehat{\mathrm{i}}-\widehat{\mathrm{j}}+5\widehat{\mathrm{k}}\mathrm{and} \overline{\mathrm{b}}=\widehat{\mathrm{i}}+2\widehat{\mathrm{j}}-3\widehat{\mathrm{k}}$ are given vectors. A vector $\overline{\mathrm{c}}$ which is perpendicular to Z-axis satisfying  $\overline{\mathrm{c}}.\overline{\mathrm{a}}=9\mathrm{and} \overline{\mathrm{c}}.\overline{\mathrm{b}}=-4$. If inclinations of   with X-axis and Y-axis are $\mathrm{\alpha }$ and $\mathrm{\beta }$ respectively, then which of the following is not true ?