hi mark090480,

The circle centre is (1,-2).

But that locates only the point at which you can place the tip of your compass.

You can now draw a circle any size you want.

The one in question has a radius of 9.

Remember, the distance formula is also Pythagoras' Theorem.

A circle is the set of all points the same distance from a fixed one.

If you take any right angled triangle