The perpendicular distance between the lines given by $(x-2 y+1)^2+\mathrm{k}(x-2 y+1)=0$ is $\sqrt{5}$, then $\mathrm{k}=$

The point of intersection of the diagonals of the rectangle whose sides are contained in the lines $x=8, x=10, y=11$ and $y=12$ is

If $m_1$ and $m_2$ are the slopes of the lines represented by $a x^2+2 h x y+b y^2=0$ satisfying the condition $16 \mathrm{~h}^2=25 \mathrm{ab}$, then ............ .