The line 2 x - y + 1 = 0 is a tangent to the circle at the point 2 , 5 and the centre of the circle lies on x - 2 y = 4 . Then, the radius of the circle is:

Step-by-step solution

Given Slope of O A = 5 - h - 4 2 2 - h = m 1 Slope of the given tangent equation = m 2 = 2 ⇒ 5 - ( h - 4 ) 2 2 - h 2 = - 1 ⇒ h = 8 Center = 8 ,   2 Radius = ( 8 - 2 ) 2 + ( 2 - 5 ) 2 = 3 5