The first quadrant of the circle has a radius of 20 units.

At 90 degrees y runs from 1 to 20 down

At circle centre x run from 1 to 20

so origin is 1,20

now place an X in position 12,6

now determine the diagonal distance :

d = sqrt ( (12-1)*(12-1) + (6-20)*(6-20) )

d = sqrt ( 317 )

d = 18 (rounded)

but X is 19 diagonal units?

Try another :

place an X in position 10,11

d = sqrt ( (10-1)*(10-1) + ( 11-20)*(11-20) )

d = sqrt (162)

d = 13 (rounded) this is correct

Try another one for a wrong answer:

place an X in position 19,20

d = sqrt ( (19-1)*(19-1) + (20-20)*(20-20) )

d = sqrt (324)

d = 18

I lost and have been doing the math all day and do not see where I am making a cock up!

Help please?

Thanks