Is it an used or a used?
Similarly, it is asked, is being used VS is used?
"It is being used" means that someone is using it at the moment. "It has been used" means that at some time in the past, somone has used it.
One may also ask, where is an used? “A” is used before words starting in consonant sounds and “an” is used before words starting with vowel sounds. It doesn't matter if the word is an adjective, a noun, an adverb, or anything else; the rule is exactly the same.
Keeping this in view, when should the word an be used?
Use “a” before words that start with a consonant sound and “an” before words that start with a vowel sound. Other letters can also be pronounced either way. Just remember it is the sound that governs whether you use “a” or “an,” not the actual first letter of the word.
Has used or had used?
"Have" and "has" are present tense verbs. "Had" is the past tense of these two verbs. In the present tense, "have" is used for I, you, we, and they and all plural nouns. "Has" is used for he, she, and it, and for all singular nouns.