When a line meets a circle

When a line meets a circle

6 marks
TGM Original Questions

The equation \(x^2+y^2+6x-4y=k\), where \(k\) is a constant, represents a circle.

  1. State the condition on \(k\) for the radius to be positive.[1]
  2. Find the value of \(k\) for which \(y=2x+1\) is tangent to the circle.[3]
  3. Find the ranges of \(k\) for which the line meets the circle at two distinct points, and for which it does not meet the circle.[2]

Solution:

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Answer:(a) \(k>-13\). (b) \(k=-\dfrac{16}{5}\). (c) Two points: \(k>-\dfrac{16}{5}\); no intersection: \(-13<k<-\dfrac{16}{5}\).

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