Is it sufficient for one who has angered his parents and then repented and pleased them that his parents implicitly forgive him, or must he explicitly ask for their forgiveness?

If a Muslim angers his parents unjustly, then regrets it and repents sincerely, and treats them kindly and virtuously, then Allah forgives whoever repents. The verse "Your Lord is most knowing of what is within yourselves. If you should be righteous, then indeed He is ever Forgiving to the oft-returning [to Him]." supports this, as does the hadith "Go back to them and make them laugh as you made them cry." So, if the child repents and his parents are pleased with him and forgive him, this is sufficient for repentance.