Hi, can someone demonstrate this ( the 1) , 2) 3) )?

Hi Can someone demonstrate this? ( the 1), 2), 3)? The first part it's just the course. Course : 2.3 coprime Integers. Definition 2. 3 Two integers a and b are coprime when god ( a, b) = 1 In this case Bezout's ( Bezout's ) theorem is started as follows. Theorem 2. 3 Two integers and b are copRime if , and only if there exist integers u and v such that aut by = 1 . what I want to prove ( the 1 ) ; 2); 3)) 1) Show that if a and b are both coprime to n, then ab is still Coprime ton. 2 ) show that if two integers a and b are coprime, the same holds for a" et b for any natural numbers im and n. 3 ) show that if a and n are two integers coprime to each other, then if theRe exists an integer U such that av= , then deduce the set -7modn of solutions of the congruence axc = b [n] in T