let the eqn of circle be (x-a)^2+(y-b)^2=r^2
as circle passes thru origin
a^2+b^2=r^2
the two lines intersect at origin and circle passes thru it
join centre of circle(a,b) to origin.
draw perpendiculars from the centre to the chords.both segments are of length 1/root 2. chords make angle 45 degree with radius.apply pyth. u get radius.