Question

Till now no one could show the full process.
So sad

Answer 1

${x}^{2} + {y}^{2} + 6x - 6y + 5 = 0 \\ {x}^{2} + 6x + 9 - 9 + {y}^{2} - 6y + 9 - 9 + 5 = 0 \\ {(x + 3)}^{2} + {(y - 3)}^{2} = 13$
therefore (-3,3) is the centre,C, of the circle
this point C (-3,3) lies on the line of the diameter
put (-3,3) in equation of diameter
2x-y+k=0
-6-3+k=0
k=9