Here's why:
* Prefix: A prefix is a word part added to the *beginning* of a word to change its meaning. Examples: "un-" in "unhappy", "re-" in "rewrite".
* Suffix: A suffix is a word part added to the *end* of a word to change its meaning or grammatical function. Examples: "-ing" in "walking", "-ly" in "quickly".
"Impolite" is a word formed from the root word "polite" with the prefix "im-".