24. Determine whether the following assertions are true or false. If true, prove the result, and if false, give a counterexample.
1. If (a, b) = (a, c) then [a,b] = [a,c]
2. If (a, b) = (a, c) then (a^2, b^2) = (a^2, c^2)
3. If (a, b) = (a, c) then (a, b) = (a, b, c)
4. If p is a prime and p | a and p | (a^2 + b^2) then p | b
5. If p is a prime and p | a^7 then p | a