Prove or disprove each of the following statements:

a. if p is prime and p divides (a^2 + b^2) and p divides (c^2 + d^2), then p divides (a^2 - c^2).

b. if p is prime and p divides (a^2 + b^2) and p divides (c^2 + d^2), then p divides (a^2 + c^2).

c. If p is prime and p divides a and p divides (a^2 + b^2), then p divides b.

help plz..dont know where to start..