"While patrick set the table", "if he is running late" and "before she boarded the plane" are the dependent clauses contained in each complex sentence.
First of all, dependent clauses, which are also known as subordinate clauses, are clauses that do not express a complete idea; therefore, they cannot be considered complete sentences. Dependent clauses can work as adjectives, nouns or adverbs. The sentences provided contain subordinate clauses that are working as adverbs. Moreover, they are modifying verbs. Sentence 1 has been introduced by the subordinating conjunction "while", whereas sentence 2 and 3 have been introduced by "if" and "before" respectively.