Proving $(A \land B) \to C$ and $A \to (B \to C)$ are equivalent 
Prove that $(A \land B) \rightarrow C$ is equivalent to $A \rightarrow (B \rightarrow C)$ in two ways: by semantics and syntax.

Can somebody give hints or answer to solve it?

Semantically you can just consider two cases.  1) Suppose A is true, and 2) Suppose A is false.  Since all atomic propositions in classical logic are either true or false, but not both, this method will work.
Syntactically, we'll need to know the proof system (the axioms and the rules of inference for your system) to know how to solve this.
