Is the word participaste the same in Brazilian and European Portuguese?

No

While the spelling and grammatical conjugation of "participaste" are identical in both varieties of Portuguese, the answer is No because the typical usage differs significantly. In Portugal, "participaste" is the standard, everyday way to address friends, family, and peers using the second-person pronoun (tu). In Brazil, the second-person conjugation is much less common in most regions; the standard way to address someone is using the pronoun você, which requires the third-person conjugation (participou). In Brazil, "participaste" is typically reserved for formal/literary writing or specific regional dialects (such as in Southern or Northern Brazil).

Brazilian Portuguese

These examples use "participaste" in the contexts where it is naturally used in Brazil: formal, literary, or specific regional dialects.

1. Tu participaste daquela importante assembleia. (You participated in that important assembly.)
2. Notou-se que tu participaste do movimento estudantil. (It was noted that you participated in the student movement.)
3. Tu participaste do congresso médico no ano passado. (You participated in the medical congress last year.)
4. Escreveu-se que tu participaste da revolta. (It was written that you participated in the revolt.)
5. Tu participaste de forma muito ativa no debate. (You participated very actively in the debate.)

Portuguese (Portugal)

These examples use "participaste" in its most natural, everyday, and informal context.

1. Tu participaste da festa? (Did you participate in the party?)
2. Tu participaste da aula de hoje? (Did you participate in today's class?)
3. Tu participaste do jogo ontem? (Did you participate in the game yesterday?)
4. Tu participaste da nossa conversa? (Did you participate in our conversation?)
5. Tu participaste do almoço com o grupo? (Did you participate in the lunch with the group?)