Let the straight lines 5x−3y+15=0 and 5x+3y−15=0 form a triangle with the x-axis. Then, the radius of the circle circumscribing this triangle is
Find the equation of circle circumscribing the quadrilateral formed by four lines 3x + 4y − 5 = 0, 4x − 3y − 5 = 0, 3x + 4y + 5 = 0 and 4x − 3y + 5 = 0