Because it is tangent to the y axis, the distance from the center of the circle to the y axis is: a, that is, the radius of the circle r = a.

So the equation of a circle can be set as: (x-a) 2+(y-b) 2 = a 2 (""stands for square).

And because the center of the circle is on x-3y=0, an equation can be obtained:

a-3b=0 - ( 1)

Then, the distance D from the center of the circle (a, b) to the straight line y=x is calculated by using the distance formula from the point to the straight line (d is represented by a, b).

Because the straight line from point to line bisects the chord, half of the circle is the root number 7.

Finally, another equation is obtained by using Pythagorean theorem:

D 2+ (radical number 7) 2 = A 2-(2)

A, b,

This will solve the problem!