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If the pair of lines $x^2-16 p x y-y^2=0$ and $x^2-16 q x y-$ $y^2=0$ are such that each pair bisects the angle between the other pair, then $\mathrm{pq}=$
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Verified Answer
The correct answer is:
$\frac{-1}{64}$
We have, equations of pair of straight lines

Now, equations of bisectors of these line are
$$
-8 p x^2-2 x y+8 p y^2=0
$$
and $-8 q x^2-2 x y+8 q y^2=0$
According to the given condition in the data, Eqs. (i) and (iv), and Eqs. (ii) and (iii) must be coincident. So,
$$
\begin{gathered}
\frac{1}{4 q}=\frac{-16 p}{1}=\frac{-1}{-4 q} \\
1=-64 p q \\
\therefore \quad p q=\frac{-1}{64}
\end{gathered}
$$

Now, equations of bisectors of these line are
$$
-8 p x^2-2 x y+8 p y^2=0
$$

and $-8 q x^2-2 x y+8 q y^2=0$

According to the given condition in the data, Eqs. (i) and (iv), and Eqs. (ii) and (iii) must be coincident. So,
$$
\begin{gathered}
\frac{1}{4 q}=\frac{-16 p}{1}=\frac{-1}{-4 q} \\
1=-64 p q \\
\therefore \quad p q=\frac{-1}{64}
\end{gathered}
$$
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