Questions & Answers about Η ακτίνα είναι χαλαρή.
Η is the definite article, meaning the.
Here it is the feminine singular nominative form, because ακτίνα is a feminine singular noun and it is the subject of the sentence.
A quick article set is:
- ο = masculine the
- η = feminine the
- το = neuter the
So Η ακτίνα = the ακτίνα.
You can tell from the words agreeing with it:
- η is feminine singular
- χαλαρή is also feminine singular
Greek adjectives and articles must agree with the noun in gender, number, and case. So even if you did not already know the gender of ακτίνα, the sentence shows it.
Also, many nouns ending in -α are feminine, and ακτίνα is one of them.