2 < α < 1 < β < 2 -2<\alpha<1<\beta<2

Algebra Level 2

-1 2 -2 1

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1 solution

Tom Engelsman
Jan 17, 2021

Let α = p p 2 + 4 2 , β = p + p 2 + 4 2 \alpha = \frac{-p -\sqrt{p^2+4}}{2}, \beta = \frac{-p+\sqrt{p^2+4}}{2} be the two roots in question. If we require 2 < α < 1 < β < 2 -2 < \alpha < 1 < \beta < 2 to hold, then we have:

2 < p p 2 + 4 2 < 1 -2 < \frac{-p -\sqrt{p^2+4}}{2} < 1 (i)

1 < p + p 2 + 4 2 < 2 1 < \frac{-p +\sqrt{p^2+4}}{2} < 2 (ii)

If we solve for p 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 + 16 3 2 < p < 0 p+2 < \sqrt{p^2+4} < p+4 \Rightarrow p^2 + 4p + 4 < p^2+4 < p^2+8p+16 \Rightarrow \boxed{-\frac{3}{2} < p < 0}

of which p = 1 \boxed{p=-1} is the only integer solution.

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