If the straight line x=0

Then the distance from the center of the circle (1, 0) to the straight line is 1= radius.

Tangent at this time, the straight line will not have two intersections with the circle, so it is not a chord.

Therefore, if there is a slope, let the straight line y=kx and the intersection point A(x 1, kx 1) be (0,0).

Substitute y=kx into the circle.

(x 1- 1)？ +k^2x 1？ = 1

Let the midpoint of the chord be (x, y)

Then 2x=x 1.

2y=y 1

Substitution acquisition

(2x- 1)？ +4y？ = 1 (x is not equal to 0)

Note that you can't get 0 o'clock, which is the biggest trap of this problem.