2005年浙江高考数学卷(理科)第20题:设点An(xn,0),Pn(xn,2n-1)和抛物线Cn:y=x2+anx+bx(n∈N),其中an=-2-4n-1/(2n-1),xn由以下方法得到:x1=1,点P2(x2,2)在抛物线C1:y=x2+a1x+b1上,点A1(x1,0)到P2的距离是A1到C1上点的最短距离…,点Pn+1(xn+1,2n)在抛物线Cn:y=x2+anx+bn上,点An(xn,0)到Pn+1的距离是An到Cn上点的最短距离.(Ⅰ)求x2及C1的方程; 2005 Zhejiang College Entrance Examination Mathematics (Science) Question 20: Set points An(xn, 0), Pn(xn, 2n-1) and Parabola Cn:y=x2+anx+bx(n∈N), where an= -2-4n-1/(2n-1), xn is obtained by: x1=1, point P2(x2,2) on parabola C1:y=x2+a1x+b1, point A1(x1,0) The distance to P2 is the shortest distance from point A1 to point C1, point Pn+1 (xn+1, 2n) is on parabola Cn:y=x2+anx+bn, point An(xn,0) to Pn+1 The distance is the shortest distance from An to Cn. (I) Find the equation of x2 and C1;