Question 23284
standard eqn. of an ellipse with foci on x axis,centre as origin  and directrices parallel to y axis is 
(X^2/A^2)+(Y^2/B^2)=1,where A and B are semi major/minor axes
foci are given by (A*E,0),(-A*E,0)
eccentricity =E =[(A^2-B^2)/A^2]^0.5
we are given the sun is at one focus and the 2 numbers you have given as 740 and 810 are  NOT ELABORATED AS TO WHAT THESE NUMBERS ARE. 

I back calculated the major / minor axes as per the answer given by you and came out		
with following interpretation of the numbers given by you.		
740 is the minimum distance of jupiter from sun	
810 is the maximum distance of jupiter from sun	
so total distance =major axis ,since sun is at one of the foci and is on x axis or major axis		
major axis =2*A=740+810=1550..or A=1550/2= 775		
as given above foci are given by (A*E,0) and (-A*E,0),with centre taken as origin.		
since sun is at focus and its coordinate is  (775-740,0) and (775-810,0) or (35,0),(-35,0) we have		
A*E=35..that is.... 775*E=35...or....E=35/775=7/155 		
further we have E=[(A^2-B^2)/A^2]^0.5		
so  B=[A^2-(E^2)(A^2)]^0.5 =A*(1-E^2)^0.5=774.2093		
hence eqn. Of ellipse is 		
(X^2/775^2)+(Y^2/774.2093^2)=1		
(X^2/600625)+(Y^2/599400)=1