Answer:
4th Option is correct.
Explanation:
Given:
x and y are the half length of the largest and smallest diameter of the ellipse.
Area of the Ellipse , a = πxy
To find: Equivalent Equation for y.
Consider,
a = πxy
πxy = a
(πx)y = a
transpose πx to RHS,

y = a ÷ ( πx )
Therefore, 4th Option is correct.