The past participle of the verb beat is beaten, and the simple past is beat. The correct form of the verb will depend on the meaning you want.
In the simple past, beat is the correct form (e.g., “Ainaz beat everybody else in the competition to claim her third gold medal”).
Use the past participle beaten to form perfect tenses and the passive voice (e.g., “She had beaten all the odds to become the leading lawyer at the firm”).
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