tomodati to kyouryokusite seikousimasita.

In this sentence, と means with.

So 友達と means with a friend / with friends.

Here, と marks the person you cooperated with. It is very common with actions done together, such as:

• 友達と話す = talk with a friend
• 家族と行く = go with family
• 友達と協力する = cooperate with a friend

So in 友達と協力して, と shows who the cooperation was with.

協力する is a suru-verb meaning to cooperate.

Its -て form is 協力して.

The -て form is used here to connect actions or ideas, similar to:

• cooperating with a friend, [we/I] succeeded
• after cooperating with a friend, [we/I] succeeded

So the sentence structure is:

• 友達と協力して = cooperating with a friend / by cooperating with a friend
• 成功しました = succeeded

The -て form often links the first action or circumstance to the main result.

成功しました is already complete and polite.

Here is the breakdown:

• 成功する = to succeed
• 成功しました = succeeded / did succeed

Because する is a verb, it gets conjugated directly. You do not add です after a normal verb.

So:

• correct: 成功しました
• incorrect: 成功しましたです

です is mainly used after nouns and -na adjectives, not after fully conjugated verbs.

成功 is originally a noun meaning success, but it can become a verb when combined with する.

So:

• 成功 = success
• 成功する = to succeed
• 成功しました = succeeded

This is a very common pattern in Japanese. Many Sino-Japanese nouns become verbs with する, for example:

• 勉強する = to study
• 練習する = to practice
• 協力する = to cooperate
• 成功する = to succeed

Japanese often leaves the subject unstated when it is understood from context.

So 友達と協力して成功しました could mean:

• I succeeded by cooperating with a friend
• We succeeded by cooperating
• He/She succeeded by cooperating with a friend

The sentence itself does not force one specific subject. You figure it out from the situation, previous conversation, or surrounding text.

This is completely normal in Japanese.

It can be either, depending on context.

Japanese nouns usually do not change form for singular vs. plural the way English nouns do. So 友達 can mean:

• a friend
• friends

If the speaker wants to make plurality clearer, they might add context or use something like 友達たち, but very often plain 友達 is enough.

So this sentence could mean either:

• cooperated with a friend
• cooperated with friends

Usually it suggests a connection between them, not just a simple list of unrelated actions.

In this sentence, 協力して naturally implies something like:

• by cooperating
• after cooperating
• cooperating, and as a result, succeeded

So the cooperation is understood as part of the reason or process leading to success.

If you only wanted to list actions more neutrally, context would matter, but here the natural reading is that cooperation contributed to the success.

Japanese word order is flexible, but this order is very natural.

The sentence goes from background information to the main result:

1. 友達と = with a friend
2. 協力して = cooperating
3. 成功しました = succeeded

So the most important final statement, succeeded, comes at the end.

You may see variations in real Japanese, especially when something is being emphasized, but this version is standard and easy to understand.

Not with the same meaning.

友達と一緒に means together with a friend, but it does not by itself express cooperation.

Compare:

• 友達と協力して成功しました
  = I/we succeeded by cooperating with a friend.

• 友達と一緒に成功しました
  = I/we succeeded together with a friend.

The second one focuses more on doing it together. The original sentence specifically highlights cooperation.

Mostly yes, but Japanese often uses 協力する in situations where English might say several different things, such as:

• work together
• help each other
• cooperate
• join forces

So 友達と協力して has a natural sense of working together with a friend.

In English, cooperate can sometimes sound a little formal depending on the context, but 協力する is very common in everyday Japanese.

Because it ends with 成功しました, which is the polite past form.

Compare:

• 成功した = plain past
• 成功しました = polite past

The polite form is commonly used in normal conversation, when speaking respectfully, in textbooks, and in many general statements.

So this sentence sounds neutral and polite, which is often the safest form for learners to use.

In many contexts, yes.

成功しました literally comes from to succeed, but natural English translations may vary depending on context:

• succeeded
• was successful
• managed to succeed

So even though the grammar is based on the verb 成功する, the best English wording may change.

That is normal in translation. The key Japanese idea is that the action/result of success happened in the past.

Sometimes it can feel close, but its core meaning is still cooperate / work together.

If the speaker mainly wants to say they received help, Japanese would more naturally use expressions like:

• 友達に手伝ってもらって = with a friend’s help / because a friend helped me
• 友達のおかげで = thanks to my friend

By contrast, 友達と協力して suggests both sides were actively working together, not just one side helping the other.