2018 GCE O level A Math Paper 2 Q9-Quadratic inequalities

This is one of the more challenging questions in the 2018 GCE O-level A-Math paper 2 on Quadratic Inequalities.
There are two parts to this question.
Part (i) is relatively simple in that we simply need to show that a given line is a tangent to a given curve.
Part (ii) is a well-known tricky question where a quadratic curve cannot be negative. This particular question is more interesting than usual because it requires the student to explain why there can only be one value of the unknown k such that the quadratic curve cannot be negative. Many students will mess up the discriminant, thinking that b^2-4ac is more than 0.
This video was recorded during one of my revision classes in 2019. It was one of our prep classes in the lead-up to the 2019 GCE O-level A-Math examination.

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