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Let α = 2 − p − p 2 + 4 , β = 2 − p + p 2 + 4 be the two roots in question. If we require − 2 < α < 1 < β < 2 to hold, then we have:
− 2 < 2 − p − p 2 + 4 < 1 (i)
1 < 2 − p + p 2 + 4 < 2 (ii)
If we solve for p in (ii), then we obtain:
p + 2 < p 2 + 4 < p + 4 ⇒ p 2 + 4 p + 4 < p 2 + 4 < p 2 + 8 p + 1 6 ⇒ − 2 3 < p < 0
of which p = − 1 is the only integer solution.