Question

I could use some help doing this simple math problem lol.

Answer 1

$D:k-9\geq 0 \wedge k\geq0\\ D:k\geq 9 \wedge k\geq0\\ D:k\geq 9\\ \sqrt{k-9}-\sqrt k=-1\\ \sqrt{k-9}=-1+\sqrt k\\ k-9=(-1+\sqrt k)^2\\ k-9=1-2\sqrt k+k\\ 2\sqrt k=10\\ \sqrt k =5\\ k=25$