Question 1197354


Latus rectum of ellipse is a straight line passing through the foci of ellipse and perpendicular to the major axis of ellipse. Latus rectum is the focal chord, which is parallel to the directrix of the ellipse. The ellipse has two foci and hence it has two latus rectums. 
Each of the latus rectum cuts the ellipse at two distinct points.
The length of latus rectum of ellipse {{{x^2/a^2 + y^2/b^2= 1}}}, is {{{2b^2/a}}}.


given:

{{{16x^2+25y^2+160x+200y+400=0}}}.............write  in standard form

{{{(16x^2+160x)+(25y^2+200y)+400=0}}}........complete squares

{{{16(x^2+10x+b^2)-16b^2+25(y^2+8y+b^2)-25b^2+400=0}}}

{{{16(x^2+10x+5^2)-16*5^2+25(y^2+8y+4^2)-25*4^2+400=0}}}

{{{16(x+5)^2-400+25(y+4)^2-400+400=0}}}..........simplify

{{{16(x+5)^2-400+25(y+4)^2=0}}}

{{{16(x+5)^2+25(y+4)^2=400}}}............divide by {{{ 400}}}

{{{16(x+5)^2/400+25(y+4)^2/400=400/400}}}

{{{(x+5)^2/25+(y+4)^2/16=1}}}

=> {{{a^2=25 }}}and {{{b^2=16}}}=> {{{a=5 }}}and {{{b=4}}}


The length of latus rectum of ellipse  is

 {{{2b^2/a =(2*16)/5=32/5=6.4}}}