Find the set of values of k for which the line 2y + x = k intersects the curve xy = 6 at two distinct points.
Solution
To find the intersection points, substitute x = k - 2y into the curve equation xy = 6:
\((k - 2y)y = 6\)
\(2y^2 - ky + 6 = 0\)
This is a quadratic in y. For two distinct points, the discriminant must be positive:
\(b^2 - 4ac > 0\)
Here, \(a = 2\), \(b = -k\), \(c = 6\).
\((-k)^2 - 4 \cdot 2 \cdot 6 > 0\)
\(k^2 - 48 > 0\)
\(k^2 > 48\)
\(k < -\sqrt{48} \text{ and } k > \sqrt{48}\)
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