Question

(p + q = 1, p2 + 2pq + q2 = 1) What the answer is ??/

Answer 1

p + q = 1
p2 + 2pq + q2 = 1

Factor the second equation:
(p + q)(p + q) = 1

From the first equation, we know that p + q = 1, so substitute 1 in for p + q once:
1(p + q) = 1
p + q = 1

q = 1 - p

This is true for every p and q such that q = 1 - p