Find the equation of a circle which is concentric with the circle `x^2 + y^2 - 4x + 6y - 3 = 0` and of double its radius.

Find the equation of a circle concentric with the circle x^2 + y^2-2x -4y + 1 = 0 and whose radius is 5.

Find the equation of the circie concentric with the circle x^2 + y^2 + 4x-8y- 6 = 0 and having radius double of its radius.

Find the equation of a circle concentric with the circle : 2x^2 + 2y^2-6x+8y+1=0 and of double its area.

Find the equation of the circle concentric with the circle x^(2) + y^(2) - 8x + 6y -5 = 0 and passing through the point (-2, -7).

Find the equation of a circle concentric with x^2 + y^2-4x -6y -3 = 0 and which touches the y-axis.

Find the equation of the circle concentric with the circle x^2 + y^2+4x+ 6y+11=0 and Passing through the point (5, 4).

Find the equation of a circle of radius 5 which lies within the circle x^2 + y^2+14x + 10y- 26 = 0 and which touches the given circle at the point (- 1, 3).

Find the equation of the circle which cuts orthogonally the circle x^2 + y^2 – 6x + 4y -3 = 0 ,passes through (3,0) and touches the axis of y.

Find the equation of the circle through points of intersection of the circle x^2 + y^2 -2x - 4y + 4 =0 and the line x + 2y = 4 which touches the line x + 2y = 0 .

Find the equation of the circle which passes through the origin and cuts off chords of lengths 4 and 6 on the circle concentric with the circle x^2+y^2-6x+12 y+15=0\ and double of its area.