Beide sind anders benutzt. ~을 해서/~으로 스트레스를 풀다: eatwas unternehmen aus der audruecklichen Absicht, den Stress abuzbauen 여행으로/여행을 통해 스트레스를 풀다: den Stress abbauen durch Reisen. 스트레스가 풀리다: Man redet von einem Stressabbau als eine eher unerwartete, erfreuliche Folge. 여행을 다녀왔더니 스트레스가 풀렸다: Nach der Reise habe ich festgestllt, der Stress war weg. ====================================================== 필요로하다 ist kein Passiv von 필요하다, denn es kann kein Passiv geben fuer das "sein" verb. Es bedeutet buchstaeblich: als erforderlich erklaeren, und entsprechend sehr viel zwingender als 필요하다. 내일까지 돌려주실 수 있죠? 내일 정말로 필요해요. Koennten Sie es bis morgen zurueckbringen? Ich brauche es morgen wirklich. 계획된 과제는 최소 백만불의 예산을 필요로 합니다. Das geplante Projekt fordert ein Budget von mindestens $1m 보이다 = sichtbar sein

Wow, I don't think about it before. But as you know, the difference between passive and active forms is about who does the action. My personal opinion is.. 스트레스를 풀다 implies a speaker's will to relieve stress, so we use this when we have much stress. "I have much pressure on me. I need to get rid of stress." We say like 스트레스를 풀어야 겠어 and 스트레스를 풀 거야. 스트레스가 풀리다 implies that the problem was solved. So we use this after we relieve stress. We say like 스트레스 완전 풀렸어 and 스트레스가 확 풀리네. So you can tell them apart thinking whether stress is relieved or not. About 보이다, we need to learn these (-이-, -히-, -리-, -기-) letters. We put them between letters of verbs to make passive forms. 보다 see -> 보이다 be seen 잡다 catch -> 잡히다 be caught 풀다 untie, relieve -> 풀리다 be untied, relieved 안다 embrace -> 안기다 be embraced So, 보이다 is used when you happen to see something or something is to be seen without/with less your will. Have a nice day/night!