The circle is sandwiched between vertical lines x = 0 and x = 12.

So, the diameter of the circle must be 12.

Its radius is 6.

With the circle being in the bottom right quadrant, its centre must be (6, -6).

Need me to draw the diagram?

May I know how did u get x=0?

x = 0, y = 0 and x = 12

x = 0 is the y axis itself

Negative y-axis is where x = 0.
Positive x-axis is where y = 0.

So if x = 0 and x = 12 are tangents to the circle, and both lines are parallel to each other, the centre is equidistant from these two lines.

Since the horizontal distance between x = 0 and x = 12 is 12 units,

The midpoint must be where x = 6
( (0 + 12)/2 )

This means x = 6 cuts through the centre of the circle and part of it is its diameter.


Now how to know the y-coordinate of the centre is -6?

Firstly, the circle lies below the x-axis and to the right of the y-axis since it is tangent to the negative y-axis and positive x-axis.

(We can say 4th quadrant)

Secondly, the diameter of the circle is now known to be 12. So the radius must be 6.

Since positive x-axis is tangent to the circle , and since y = 0 on this axis,

Then the highest point of this circle is at y = 0.

Shift 6 units down, we get y = -6. This is where the centre lies on.

The intro to the story feels like the 2015 O Level question...

Did the textbook steal the idea from there? Hmm...

I wouldn't use the word steal. That suggests copyright infringement. These type of questions can be easily thought of, similarity (or even adaptation of the question) is common

Weirdly enough I realised that for new concepts not previously found in textbooks but seen in the O Levels, the publishers are ready to adapt the ideas and put them into the books.

Keeping up with Cambridge, who is always ahead in coming up with novel questions. This one is hardly novel anyway

Amaths 360 2nd edition textbook motivates the students to learn the concepts very deeply. It can get challenging mostly. Because of u guys helping, I dare to attempt them. Thanks a lot

It is long overdue. Past batches always are taught drill and practice and the conceptual understanding is neglected.

I find 2nd edition more clear cut in purpose than the Ist edition.