posted by rfvv .
1. The problem is so difficult that I cannot solve it.
2. The problem is too difficult for me to solve.
3. It is too difficult for me to solve the problem.
(Are the three sentences the same? Do they come from the same structure? Can we omit 'that' in Sentence 1?)
They all mean the same thing, and are grammatically correct. If "that" is removed from #1, the sentence would still be understood in conversation, but it is better if "that" were there when writing it. It would be an "implied" if it were omitted.
I believe the 3rd sentence doesn't mean the same as the other two. The 3rd states that it is difficult for the person to solve. (who knows why...) the other two clearly state the problem is too difficult
I agree with DrWLS.