Question: Suppose that f(x) = x 3 px2 + qx and g(x) = 3x 2 2px + q for some positive integers p and q. (a)
Suppose that f(x) = x
3 px2 + qx and g(x) = 3x
2 2px + q for some positive
integers p and q.
(a) If p = 33 and q = 216, show that the equation f(x) = 0 has three distinct
integer solutions and the equation g(x) = 0 has two distinct integer solutions.
(b) Suppose that the equation f(x) = 0 has three distinct integer solutions and the
equation g(x) = 0 has two distinct integer solutions. Prove that
(i) p must be a multiple of 3,
(ii) q must be a multiple of 9,
(iii) p
2 3q must be a positive perfect square, and
(iv) p
2 4q must be a positive perfect square.
(c) Prove that there are infinitely many pairs of positive integers (p, q) for which
the following three statements are all true:
The equation f(x) = 0 has three distinct integer solutions.
The equation g(x) = 0 has two distinct integer solutions.
The greatest common divisor of p and q is 3 (that is, gcd(p, q) = 3).
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