Question 1
In square $ABCD$, $E,F$ are points on the sides $AB$ and $BC$ respectively. Let $N$ be the foot of the perpendicular from $B$ onto $CE$. The circular arc from $C$ to $A$ centred at $B$ with radius $BC$ intersects the segment $DN$ at $K$. If $\angle FND=90^\circ$ and $KF$ is parallel to $NB$, find the value of $\dfrac{BE+BF}{AB}$.