Hi Mr Eric, thanks for helping me with the other 2 qns. Even though I eventually find out how to do Q7 on my own, but I just double-checked my method with your solution.

For Q9 (iii), I asked my teacher about it too. But when he said use the original equation (that is ax^2 + 5x + a - 5) and just discriminate it, I was quite confused.
Because I did like what you did above (substitute y=x-2 into ax^2 + 5x + a - 5), I don’t know if what my teacher mentioned can also be one of the ways to solve this qn.

Good morning Irah! I’m pretty sure by discriminant he actually meant for you to simul the equations first. It is meaningless to do discriminant on that equation ax2 + 5x + a - 5 alone because the question wants us to find out the values of a for which the line y = x - 2, and not y = 0, is a tangent to the curve.