Learn Hardcore Korean: chinguege keikeureul sa dallago butakhaesseoyo.

에게 is the dative case marker that indicates the person who is the target or recipient of an action—here, the friend you are addressing. In spoken Korean, you can also use 한테 (친구한테) with the same meaning, though 에게 is slightly more formal.

Why is 케이크 marked with 를 in 케이크를?

Because 사다 (“to buy”) is a transitive verb and takes a direct object, which is marked by -을/를. Thus 케이크를 사다 literally means “to buy a cake,” with 케이크를 serving as the thing being bought.

Explain how 사 달라고 works in this sentence.

사 달라고 comes from the grammar pattern -(아/어) 달라고 하다, which means “to ask someone to do something for you.”
• 사 = the verb stem “buy” (from 사다)
• -아/어 달라고 = “(I) ask (you) to … for me” + quotation marker -고
So 사 달라고 literally embeds your request “buy (it) for me” before the main verb 부탁했어요.

Couldn’t we use 사 주라고 부탁했어요 instead of 사 달라고 부탁했어요? What’s the difference?

They’re very close but have a subtle shift in perspective:
• 사 달라고 부탁했어요 uses 달라고 (“give it to me”), so you’re asking the friend to buy it for you.
• 사 주라고 부탁했어요 uses 주라고 (“give it to someone else”), so you would be asking your friend to buy it for a third person.
In short, 달라 = “give to me,” 주라 = “give to someone else.”

What exactly does 부탁했어요 mean?

부탁하다 means “to request a favor” or “to ask someone for help.” 했어요 is the polite past tense, so 부탁했어요 translates to “(I) asked (for a favor).” In this sentence, it refers to the act of asking the friend to buy the cake.

Why is the sentence in past tense (부탁했어요) rather than present (부탁해요)?

Using the past tense 부탁했어요 indicates that the request has already been made. If you want to say “I’m asking (right now),” you’d use 부탁해요:
• 친구에게 케이크를 사 달라고 부탁해요. (I’m asking my friend to buy me a cake.)

How would you translate the full sentence literally and naturally?

• Literal word‐for‐word: “(I) to friend cake buy-for-me-that asked (a favor).”
• Natural English: “I asked my friend to buy me a cake.”

Is 친구한테 equally acceptable instead of 친구에게?

Yes. 친구한테 is more casual and common in everyday speech, while 친구에게 is a bit more formal or written. Both mean “to my friend.”