\ x_1=\frac{-2}{q}\\
x_4=x_1*q^3=-6\ =>\ x_1=\frac{-6}{q^3}\\
\frac{-2}{q}=\frac{-6}{q^3}\\
q=\sqrt3\\
x_7=x_1*q^6=x_1*q*q^5=x_2*q^5\\
x_7=-2*(\sqrt3)^5=-2*9\sqrt3=-18\sqrt3" alt="x_n=x_1*q^{n-1}\\
x_2=x_1*q=-2\ =>\ x_1=\frac{-2}{q}\\
x_4=x_1*q^3=-6\ =>\ x_1=\frac{-6}{q^3}\\
\frac{-2}{q}=\frac{-6}{q^3}\\
q=\sqrt3\\
x_7=x_1*q^6=x_1*q*q^5=x_2*q^5\\
x_7=-2*(\sqrt3)^5=-2*9\sqrt3=-18\sqrt3" align="absmiddle" class="latex-formula">