Given a1=729 , a2= -243
Common ratio r= a2/a1= -243/729
r= -1/3
[tex]\begin{gathered} \text{For a geometric sequence, } \\ a_n=a_1r^{n-1} \\ a_7=\text{ 729(}\frac{-1}{3})^{7-1} \\ =729(\frac{-1}{3})^6 \\ 729\text{ (}\frac{1}{729}) \\ =1 \end{gathered}[/tex]