find the equation of the tangent at (0,2) to the circle with equation

题目

find the equation of the tangent at (0,2) to the circle with equation
(x+2)平方 + (y+1)平方=13

答案

(x+2)平方 + (y+1)平方=13的圆心为（-2,-1）,所以过圆心和(0,2)的直线斜率为：[2-(-1)]/(0-(-2))=3/2,所以切线方程显然与过圆心和(0,2)的直线斜率互为负倒数：所以为：-1/（3/2）=-2/3,已知斜率和过(0,2)点的条件,可...