Although it is known that the straight line (proportional function) y=-( 1/2)x passes through the origin,

However, it is known that the straight line y=-( 1/2)x and the parabola y=-( 1/4)x square +6 intersect at two points A and B, but the middle perpendicular of the line segment AB does not pass through the origin.

Solve the equation:

y=-( 1/2)x？ ( 1)

y=-( 1/4)x+6？ (2)

get

The intersection of a straight line and a parabola is A(6, -3) and b (-4, 2).

The midpoint of line AB is C( 1,-1/2).

The analytical formula of the midline of the line segment AB is y=2x-5/2.

The analytical formula of the midline of the line segment AB is 4x-2y-5=0.