A geometric sequence has a common ratio. Let that ratio be r. Then you get the sequence:
[tex]45,45r,45r^{2}[/tex]
You know that the third term is 1620, so just solve for r:
[tex]45r^{2}=1620 \\
r^{2}=36 \\
r=\pm6[/tex]
So the common ratio is either 6 or -6. That means there are two possible missing terms:
[tex]45r \\
=45(\pm6) \\
=\pm270[/tex]
