Question

Hipparchus, originator of trigonometry, began measuring distances between celestial bodies in the 2nd century BCE.

Identify the appositive phrase.

Answer 1

An appositive phrase is usually set off from the rest of the sentence by using commas, and it functions as an adjective, meaning that it describes the subject of the sentence.
Having this in mind, the appositive phrase here is originator of trigonometry.