The value of `K` .If the circles `x^(2)+y^(2)+2by-k=0,x^(2)+y^(2)+2ax+8=0` are orthogonal

If the circles x ^(2) + y ^(2) + 5x -6y-1=0 and x ^(2) + y^(2) +ax -y +1=0 intersect orthogonally (the tangents at the point of intersection of the circles are at right angles), the value of a is

Find the locus of the centres of the circle which cut the circles x^(2)+y^(2)+4x-6y+9=0 and x^(2)+y^(2)+4x+6y+4=0 orthogonally

For what value of k is the circle x^(2)+y^(2)+5x+3y+7=0 and x^(2)+y^(2)-8x+6y+k=0 cut each other orthogonally.

The value of k so that x^(2)+y^(2)+kx+4y+2=0 and 2(x^(2)+y^(2))-4x-3y+k=0 cut orthogonally, is