Area of ellipse
\(A=\pi r_1 r_2\)
\(\because r_1=a-a e=a(1-e)\)
\(\text { and } r_2=a+a e=a(1+e)\)
\(A=\pi\{a(1-e)\}\{a(1+e)\}\)
\(=\pi a^2(1-e)(1+e)\)
\(=\pi a^2\left(1^2-e^2\right)\)
\(\because e^2 \ll a^2 \text { then }\)
\(A=\pi a^2\)
\(\text { So, } a \propto A^{1 / 2}\)
\(\text { According to Keplar's \)III\( law }\)
\(T^2 \propto a^3\)
\(T^2 \propto\left[(A)^{1 / 2}\right]^3\)
\(T^2 \propto A^{3 / 2}\)
\(A \propto\left(T^2\right)^{2 / 3}\)
\(A \propto T^{4 / 3}\)
($G$ ગુરુત્વાકર્ષણનો અચળાંક ; $\mathrm{M}$પૃથ્વીનું દળ)