Hello Rgesh. Given values for perimter 'P' and semi-axis 'y' you can rearrange the equation to get a quadratic equation in the other semi-axis 'x':

Bring the pi factor to the left hand side and square both sides, and expand the (x-y)^2 term:

Now gather terms to make a quadratic in x:

Now you can apply the quadratic formula to solve for x. The equivalent equation for y, given values for x and P, is: