Use the distance formula:
x2 is 1 and x1 is -2
y2 is root7 and y1 is 0
Point (X1,Y1) is basically the coordinate of the centre point of the circle
Point (X2,Y2) is the point that on the circle
So if the point(1,root7) is on the circle, the final distance you get should be the radius of the circle, which is 4 units
Calculate it and you can get the answer that is 4
Therefore the point (1,root7) is on the circle
