题目
Problem
The equation of a circle is x2+y2+4x−8y−12=0.
(a) Find an equation of the tangent to the circle at the point (2,8), giving your answer in the form ax+by+c=0.
[4]
(b) Given that the line x+3y=k does not intersect the circle, show that k2−20k−220>0.
[5]
题目中文翻译
一个圆的方程为 x2+y2+4x−8y−12=0。
(a) 求该圆在点 (2,8) 处的切线方程，答案写成 ax+by+c=0 的形式。
(b) 已知直线 x+3y=k 不与该圆相交，证明 k2−20k−220>0。
解答
