20 1 1 Zhejiang Science College Entrance Examination Mathematics No.265438 +0

(2 1)(2 1) (full mark of this question 15) Known parabola = and the center of the circle is point m.

(i) Find the distance from point m to parabolic directrix;

(2) It is known that point P is a point on a parabola (different from the origin), and point P is two tangents of a circle, which intersect with the parabola at point A and point B respectively. If the straight line passing through point M and point P is perpendicular to AB, the equation of the straight line is found.

(1) Solution: According to the meaning of the question, the equation of the parabola directrix is: So the distance from the center of the circle m (0,4) to the parabola is

(2) Solution: Let P(x0,

X02), A()B (), the tangent equation between circle C2 and point p is y-x0=k(x-

x0)

That is to say,

①

rule

that is

Let the slopes of PA and PB be the above two equations, so

Replace it with ①,

Because it is the root of this equation, so

Get from MP⊥AB, get.

That is, the coordinate of point P is 0, so the equation of straight line L is 0.