If the circles `x^2+y^2+10x+8y+c=0 and x^2+y^2-10x-8y+c=0` cut onbogonally, then the value of `''C''` is

Circles x^2+y^2-2x-4y=0 and x^2+y^2-8y-4=0

The circles x^2+y^2-6x-8y+12=0, x^2+y^2-4x+6y+k=0 , cut orthogonally then k=

The circles x^2+y^2-6x-8y+12=0, x^2+y^2-4x+6y+k=0 , cut orthogonally then k=

If the circles x ^(2) + y ^(2) - 8x - 6y + c= 0 and x ^(2) + y ^(2) - 2y + d =0 cut orthogonally, then c + d equals

If the radical axis of the circles x^(2)+y^(2)-6x-8y+c=0 and x^(2)+y^(2)-8x-6y+c=0 passes through (-1,1) then find the value of c

If the circles x^(2) + y^(2) - 6x - 8y + 12 = 0 , x^(2) + y^(2) - 4x + 6y + k = 0 cut orthogonally, then k =