Make an alphabet searchlight!

R, 67 55 bytes

for(i in 26:1)cat(rep(" ",i-1),LETTERS[i:1],"
",sep="")

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05AB1E, 7 bytes

Code:

₂žp.s1Λ

Uses the 05AB1E encoding. Try it online!

Explanation

 žp.s      # Get the suffixes of ZYX...CBA
      Λ    # Using the canvas mode, print the
₂          # first 26 elements of the array
     1     # into the upper-right direction

Python 2, 57 bytes

i=26
while i:i-=1;print' '*i+bytearray(range(65+i,64,-1))

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