If $P(x_1, y_1)$ and $Q(x_2, y_2)$ are the two points on a plane, then the change in $x$ and $y$ coordinates is denoted by $∆x$ and $∆y$ respectively. Therefore, $x = ∆x = x_2 - x_1$ and $y = ∆y = y_2 - y_1$. The quantities $∆x$ and $∆y$ may be positive, negative or zero. For example, when $x_2 > x_1$ then $∆x$ is positive and if $x_2 < x_1$ then $∆x$ is negative.
I want to ask that if $x_1$ and $x_2$ both lie in the first quadrant then they will both be positive, and the change in $x$ will be positive. If we say that $x_1 = 4$ and $x_2 = 3$ then the change in $x$ will be negative. I think, the passage which I've quoted above says that if the point $Q$ lies in the $II$ or $III$ quadrant then $x_2 < x_1$, but if they $P$ and $Q$ lie in the $I$ quadrant then the value which is greater, say $Q$ will have $x_2$ coordinate, and the smaller one will have $x_1$ coordinate. Am I right? Please help me with my confusion.