1. A chord $P Q$ is drawn through the focus $F$ of the parabola $y=a x^{2}(a<0)$. If $|P F|=2007,|Q F|=10$, then, $a=$ $\qquad$
$$
\text { II.1. }-\frac{10280}{2017} \text {. }
$$

Let the distance from the focus to the directrix be $p$, and
$$
|P F|=2007=x,|Q F|=10=y \text {. }
$$

From the similarity of the two triangles in Figure 3, we have
$$
\begin{array}{l}
\frac{x-p}{p-y}=\frac{x}{y} . \\
\text { Therefore, } p=\frac{2 x y}{x+y} \\
=\frac{50140}{2017} .
\end{array}
$$

Thus, $a=-2 p=-\frac{10280}{2017}$.