Confirm it's a Cartesian translation (9)
I believe the answer is:
ascertain
'confirm' is the definition.
(I know that ascertain is a more specific form of the action verify)
'a cartesian translation' is the wordplay.
'translation' is an anagram indicator.
'cartesian' is an anagram of 'ASCERTAIN'.
'it's' acts as a link.
(Other definitions for ascertain that I've seen before include "Find out for sure, determine" , "Establish, find out" , "settle" , "Prove" , "Establish after an investigation or study" .)