Equation of chord with given middle point is given by,
T=S1
⇒25x+40y=251+1001
⇒2008x+5y=2008+2
⇒y=510−8x..(i)
⇒25x2+400(10−8x)2=1
⇒40016x2+100+64x2−160x=1
⇒4x2−8x−15=0
⇒x=88±304
⇒x1=88+304;x2=88−304
Similarly, y=510−8±304=52±304
⇒y1=52−304;y2=52+304
Distance =(x1−x2)2+(y1−y2)2
=644×304+254×304
=51691