The tangent line passing through a circle x ^ 2 + y ^ 2 = 4 and a point P (2,1) leading to the circle is obtained

The tangent line passing through a circle x ^ 2 + y ^ 2 = 4 and a point P (2,1) leading to the circle is obtained

So the distance from the tangent to the center of the circle (0,0) is the radius of the circle 2. = = = > | 1-2k | / √ (1 + K ^ 2) = 2. The solution is k = - 3 / 4. The tangent equation is 3x + 4y-10 = 0. (2) when the tangent slope does not exist, it is obvious that the line x = 2 passes through the point (2,1) and is tangent to the circle x ^ 2 + y ^ 2 = 4. Therefore, the line x = 2 is also the tangent of the circle