Is it a geometric sequence or not?

Jelly, 4 bytes

Ṣ÷ƝE

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Thanks to fireflame241 for pointing out a mistake

How it works

Ṣ÷ƝE - Main monadic link, takes an array as input
     - e.g                            A = [2, 8, 4] or   A = [2, 6, 14]
Ṣ    - Sort                               [2, 4, 8]          [2, 6, 14]
  Ɲ  - Over overlapping pairs [x, y]...   [[2, 4], [4, 8]]   [[2, 6], [6, 14]]
 ÷   - ...divide x by y?                  [0.5, 0.5]         [0.33, 0.43]
   E - Is the list all the same?          1                  0

J, ^{15 14} 13 bytes

1=&#&=2%/\/:~

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-1 byte thanks to xash

-1 byte thanks to Bubbler

• 1= Does one equal...
• &#&= the length of the uniq of...
• 2%/\ the list created by dividing each element by its right neighbor in the input list...
• /:~ sorted.

APL (Dyalog Unicode), 25 19 bytes

{~∨/⌈(⊣-⊃)2÷/⍵[⍋⍵]}

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-6 bytes thanks to @Adám

⍵[⍋⍵]      ⍝ sort ⍵
2÷/        ⍝ Take the quotient of all consecutive pairs
           ⍝ Check if all are equal:
(⊣-⊃)       ⍝ Subtract the first quotient
~∨/⌈        ⍝ Are all 0?