Final Answer:  
If 
 and
 and 
 , then
 , then 
 : states that if
 : states that if 
 divides
 divides 
 and
 and 
 divides
 divides 
 , then
 , then 
 also divides
 also divides 
 .
 . 
Step-by-step explanation:
The proof begins by supposing 
 and
 and 
 . By the definition of divisibility,
 . By the definition of divisibility, 
 means that
 means that 
 for some integer
 for some integer 
 , and
 , and 
 means that
 means that 
 for some integers
 for some integers 
 . Substituting
 . Substituting 
 into
 into 
 results in
 results in
 . The definition of divisibility states that if
. The definition of divisibility states that if 
 , with
 , with 
 being an integer, then
being an integer, then 
 . Thus, the initial assumption that
 . Thus, the initial assumption that 
 and
 and 
 leads to
 leads to 
 .
 .
In detail, assuming 
 implies
 implies 
 for some integer
 for some integer 
 . Also, assuming
 . Also, assuming 
 implies
 implies 
 . Substituting
 . Substituting 
 into
 into 
 gives
 gives
 . According to the definition of divisibility, if
. According to the definition of divisibility, if 
 , where
 , where 
 is an integer, then
 is an integer, then 
 . Therefore, the conditions
 . Therefore, the conditions 
 and
 and 
 lead logically to
 lead logically to 
 , as demonstrated by the substitution and the definition of divisibility. This confirms that if
 , as demonstrated by the substitution and the definition of divisibility. This confirms that if 
 and
 and 
 , then
 , then 
 based on the transitive property of divisibility.
 based on the transitive property of divisibility.