Let $P^2+Q^2\gt 0$ ,$P_x=Q_{y'}$ and $P_y=-Q_{x'}$ then proof that the equation
$$P(x,y)+y'Q(x,y)=0$$
has the multiplicator $(P^2+Q^2)^{-1}$
I dont understand whats meant by $Q_{x'}$ or$P_x=Q_{y'}$ . $P_x$ is the partial derivative with respect to x and is $Q_{x'} =\frac{d^2}{d^2x}Q$ ?
Has anyone seen that particular Notation because I havent.
Would appreciate an Explanation.