1.

 If x2 + y2 - 4x - 4y - k = 0 is the equation of the locus of the point from which perpendicular tangents can be drawn to the circle x2 + y2 - 4x - 4y = 0, then the value k is .......

Answer»

The equation

x2 + y2 - 4x - 4y = 0   ...(i)

 represents a circle with centre (2, 2) and radius 8 = 22 . Then the locus of point from which perpendicular tangents can be drawn to the circle given in Eq. (1) is a concentric circle whose radius is 2 times the radius of the circle [this circle is called the director circle of the circle given in Eq. (1).

Hence, the radius of the director circle is 2(22) = 4. Thus k = 8.



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