Let `R` be the distance of the Earth from the sun when the Earth is at the position, perpendicular to the major axis of its elliptical orbit as shows in Fig.
From the property of ellipse, we have
`(1)/(R ) + (1)/(R ) = (1)/(r_(1)) + (1)/(r_(2))` or `(2)/(R ) = (r_(1) + r_(2))/(r_(1) r_(2))`
or `R = (2r_(1)r_(2))/(r_(1) + r_(2))`