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The phonetics may be useful in a dictionary book to know the pronunciation, however I have to say that I found big mistakes in well known French dictionaries, the best to use is Le Petit Robert.
Patte (leg for animal)
Laver (to wash)
Pâte (pasta, pastry)
Rule for the second A:
a- The circumflex accent on the letter: â
b- The sound “a” is isolated at the end of the word:
Chat (we don’t pronounce the “t”)
Gars (we don’t pronounce “rs”)
c- The origin of the word may explain the pronunciation:
“Passer” comes from “pas” (step) and we keep the same pronunciation for the verb.
However, “chasser” (to hunt) has not the same “a” because it comes from “chasse” (the most common “a”).