The chord of parabola $y^2=4ax$ is $y=\sqrt{2}x-4a\sqrt{2}$. then length of this chord is 

On substituting value of   from chord to parabola, we 

${(\sqrt{2}x-4a\sqrt{2})}^2=4ax\Rightarrow x^2-100x+16a^2=0\Rightarrow x=8a\&2a$

On putting these values in chord, we get values of  $y$

$y=+4\sqrt{2}a\&-2a\sqrt{2}$

$\therefore$length of chord is $\sqrt{{(8a-2a)}^2+{(4\sqrt{2}a+2\sqrt{2}a)}^2}=6\sqrt{3}a$