Answer:
Indicating he passed the exam, Jackson gave a thumbs-up to his friends.
After an hour, Jackson let his friends know he passed the exam.
Step-by-step explanation:
A participle phrase is a group of words containing a participle, modifier, and pronoun or noun phrases. The Pronoun/Noun will act the recipient of the action in the phrase. You need a comma after a Participle Phrase if it comes at the beginning of a sentence and the following phrase is a complete sentence.