If  $(x_1,y_1)and(x_2,y_2)$ are end points of  a focal chord of the parabola  $y^2=5x$ then $4x_1{x}_2+y_1{y}_2=$

$\begin{array}{l}{y}^2=5x\Rightarrow 4a=5\\ \Rightarrow a=\frac{5}{4}\\ x_1{x}_2=a^2{y}_1{y}_2=-4a^{2}4x_1{x}_2+y_1{y}_2=4\times \frac{25}{16}-\frac{25}{4}=0\\ =\frac{25}{16}=-4\times \frac{25}{16}\\ =-\frac{25}{4}\end{array}$