Question 4
Let $ABCD$ be a parallelogram. Points $X$ and $Y$ lie on segments $AB$ and $AD$ respectively, and $AC$ intersects $XY$ at point $Z$. Prove that
$$
\frac{AB}{AX} + \frac{AD}{AY} = \frac{AC}{AZ}
$$
$$
\frac{AB}{AX} + \frac{AD}{AY} = \frac{AC}{AZ}
$$