Answer
$1728, 1296, 972$
Work Step by Step
A geometric sequence is a sequence whose terms are obtained by multiplying each term by the same fixed constant $r$ to get the next term.
A geometric sequence has the form
$a, ar, ar^{2}, ar^{3}, \ldots$
The number $a$ is the first term of the sequence, and the number $r $is the common ratio.
The nth term of the sequence is $\quad a_{n}=ar^{n-1}$
--------------
Given: $r=0.75,\quad a_{4}=729,$
Using $a_{n+1}=a_{n}r$, we work our way back...
$a_{4}=a_{3}r$ leads to
$a_{3}=729\div 0.75=972$
$a_{3}=a_{2}r$ leads to
$a_{2}=972\div 0.75=1296$
$a_{2}=a_{1}r$ leads to
$a_{1}=1296\div 0.75=1728$
