\(\Leftrightarrow\left(x-y+m\right)^2+y^2+2\left(m+1\right)y-m^2+25\ge0\); \(\forall x;y\)
\(\Leftrightarrow y^2+2\left(m+1\right)y-m^2+25\ge0\) ;\(\forall y\)
\(\Leftrightarrow\Delta'=\left(m+1\right)^2-\left(-m^2+25\right)\le0\)
\(\Leftrightarrow m^2+m-12\le0\Rightarrow-4\le m\le3\)