이르다, 다다르다 차이가 뭐에요?
Both mean "arrive", so is there anything difference between them? And which one has the same meaning with 도착하다?

Question

Answer

Both can be used as "도착하다" but they also can use as "reach to somewhere" or "reach to something"

for example 그는 체력의 한계에 이르렀다(past verb of 이르다) = " "He faced his physical limit."
                                                다다랐다.(Past verb of 다다르다)

or         우리는 결론에 이르렀다.(Past verb of 이르다)= " We finally reached to the conclusion"
                                        다다랐다(Past verb of 다다르다)

They all normally used in written Korean. So in everyday Korea, I recommend you to use 도착하다 when you want to express "arrive" in Korean

Cheers

DK