watashi no heya no tonari ni tomodachi ga sunde imasu.

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Breakdown of watashi no heya no tonari ni tomodachi ga sunde imasu.

• 友とも達だち: friend
• が: subject particle
• の: possessive case particle

Questions & Answers about watashi no heya no tonari ni tomodachi ga sunde imasu.

What is the function of the two の particles in 私の部屋の隣に友達が住んでいます?

The first の marks possession: AのB means “B of A,” so 私の部屋 = “my room.”
The second の links 部屋 with 隣 to form “the area next to X”: Bの隣 = “next to B.”
Together, 私の部屋の隣 means “next to my room.”

Why is に used after 隣 instead of で?

In Japanese, に indicates the location where something exists or someone resides (with verbs like います or 住んでいます).
で marks the place where an action occurs (e.g. 公園で遊ぶ “play in the park”).
Since 住んでいます is about residence/existence, you use に:
隣に住んでいます “lives next door.”

Why do we use が in 友達が住んでいます, rather than は?

Existential verbs like います/あります typically take が to mark what exists or lives:
～がいます = “there is/are (someone).”
Using は would turn 友達 into the topic and imply contrast or further comment.
Here が simply presents new information: “(A) friend lives next door.”

What does 住んでいます mean here? Why not just 住みます?