Problem: Find the general integral of the partial differential equation
\[
(2xy - 1)p + (z - 2x^2)q = 2(x - yz)
\]
and also the particular integral which passes through the line $x =1, y = 0$.
The auxiliary equations are
\[\frac{\mathrm{d} x}{2xy - 1} = \frac{\mathrm{d} y}{z - 2x^2} = \frac{\mathrm{d} z}{2(x - yz)}.\]
Choose the multipliers $(2x, 2y, 1)$ and $(z, 1, x)$.
Solution: The given partial differential equation is
\begin{equation}\label{eq:18Apr2025-1}
(2xy - 1)p + (z - 2x^2)q = 2(x - yz).
\end{equation}
So, the auxiliary equations are
\begin{equation}\label{eq:18Apr2025-2}
\frac{\mathrm{d} x}{2xy - 1} = \frac{\mathrm{d} y}{z - 2x^2} = \frac{\mathrm{d} z}{2(x - yz)}.
\end{equation}
We recall that for a given partial differential equation $Pp + Qq = R$, we have
\[
\frac{\mathrm{d} x}{P} = \frac{\mathrm{d} y}{Q} = \frac{\mathrm{d} z}{R} = \frac{S \mathrm{d} x + T \mathrm{d} y + U \mathrm{d} z}{SP + T Q + UR},
\]
where $S,T,U$ are functions of $x,y,z$. We call $(S, T, U)$ a multiplier and we choose this so that $SP + T Q + UR = 0$. Then we have $S \mathrm{d} x + T \mathrm{d} y + U \mathrm{d} z = 0$.
Consider the multipliers, $(2x, 2y, 1)$, then we have
\begin{align*}
\frac{2x \mathrm{d} x + 2y \mathrm{d} y + \mathrm{d} z}{2x(2xy - 1) + 2y(z - 2x^2) + 2(x - yz)} = \frac{2x \mathrm{d} x + 2y \mathrm{d} y + \mathrm{d} z}{0}.
\end{align*}
This implies
\[
2x \mathrm{d} x + 2y \mathrm{d} y + \mathrm{d} z = 0 \implies x^2 + y^2 + z = c_1,
\]
where $c_1$ is a constant.
Again choose a multiplier $(z, 1, x)$, we have
\[
\frac{z \mathrm{d} x + \mathrm{d} y + x \mathrm{d} z}{z(2xy - 1) + (z - 2x^2) + 2x(x - yz)} = \frac{z \mathrm{d} x + \mathrm{d} y + x \mathrm{d} z}{0}.
\]
Thus, we have
\begin{align*}
z \mathrm{d} x + \mathrm{d} y + x \mathrm{d} z = 0 & \implies d(xz + y) = 0 \\
& \implies xz + y = c_2,
\end{align*}
where $c_2$ is a constant. Thus, a general solution will be
\begin{equation}\label{eq:18Apr2025-3}
f\left( x^2 + y^2 + z, xz + y \right) = 0,
\end{equation}
where $f$ is any arbitrary function.
Now to find a particular integral, we have $x = 1, y = 0$ which implies
\begin{align*}
c_1 = z + 1 \quad \text{ and } \quad c_2 = z \implies c_1 = c_2 + 1.
\end{align*}
Thus, a particular integral will be
\[
x^2 + y^2 + z - xz - y - 1 = 0 .
\]