20. Sequences, Series & Induction

Write a recursive formula for the geometric sequence $\(\left\)\(\lbrace\)18,6,2,\(\frac\)23,\(\ldots\[\right\]\rbrace\)$.

Find the $10^{\(\th\)}$ term of the geometric sequence in which $a_1=5$ and $r=2$.

Write a formula for the general or $n^{\(\th\)}$ term of the geometric sequence where $a_7=1458$ and $r=-3$.