[m]=\frac{18-6\cdot (a^{\frac{1}{2}}+3)}{a^{\frac{1}{2}}\cdot (a^{\frac{1}{2}}+3)}=\frac{18-6\cdot a^{\frac{1}{2}}-18}{a^{\frac{1}{2}}\cdot (a^{\frac{1}{2}}+3)}=\frac{-6\cdot a^{\frac{1}{2}}}{a^{\frac{1}{2}}\cdot (a^{\frac{1}{2}}+3)}=-\frac{6}{a^{\frac{1}{2}}+3}[/m]