hi every one

can any one help me to prove the following problem

Assuming thatr is a primitive root of the odd prime p, establish the following fact

a) the congruence r^((p-1)/2) =-1(mod p) holds.

b) if r' is any other primitive root of p , then rr' is not primitive root of p.

c) if the integer r' is such that rr'=1(mod p) then r' is primitive root of p.

and thnx alot