Direction of x-axis with respect to y-axis in Cartesian coordinate system? What should be the direction of y-axis with respect to x-axis in cartesian coordinate system ?
It should be on right hand side or left hand side of x-axis or it can be on both sides as long as it is perpendicular to x-axis ?
Plus
Angles in counterclockwise rotation are considered positive when they are measured from positive x-axis. What if the rotation is clockwise ? From which axis the angles will be considered positive if the rotation is clockwise ? 
 A: It is solely matter of convention, in one case we talk of Right Hand System in the second of Left Hand System, note indeed that we need also to fix a z axes direction to define a clockwise and a counterclockwise direction for rotation.


A: The $x$-axis (also known as the abscissa) goes horizontally and the $y$-axis (also known as the ordinate) goes vertically. This is because, $$\begin{align} x &= \text{ the independent variable; and} \\ y &= \text{ the dependent variable.}\end{align}$$ This means that from these, we can measure data (typically for scientific purposes) and graph equations. When conducting a science experiment, we look at cause and effect, and how $$\text{Cause}\longrightarrow\text{Effect}.$$ Here, there are two variables in our experiment. The variable that creates the cause, namely $x$, and the variable that becomes the effect of that cause, namely $y$. $$\underbrace{\text{Cause}}_{x} \longrightarrow\underbrace{\text{Effect}}_{y}.$$ It follows, then, that the variable $y$ depends on that of $x$, and so is dependent, with $x$ being vice versa (namely independent).
There are other elements under investigation during a scientific experiment, but this is where the graph originated from, and we just applied it mathematically by writing out an equation to describe the relationship between the cause and effect (the $x$ variable to the $y$ variable). For different forms of equations, we have different relationships. For example, the equation $$y = mx + c$$ describes the linear relationship between $x$ and $y$. And the equation, $$y = ax^2 + bx + c$$ describes the quadratic relationship between $x$ and $y$. We graph these equations from plotting points on our graph, for which their position on the graph corresponds to an $x$ point and a $y$ point. We represent this as a coordinate $(x, y)$. Notice that this word derives from the word ordinate which is the $y$-axis. However, when we have a coordinate $(x, y)$ that is not plotted on the graph, this is known as an ordered pair. This is necessary because we can write equations like, $$\text{Find $(x, y)$ over the integers if $y^2 = 2x^2 - 1$}.\tag*{$\bigg(\begin{align} &\text{This is a negative Pell} \\ &\text{equation by the way.}\end{align}\bigg)$}$$ Now we also have a third axis, namely the $z$-axis, to form ordered triplets $(x, y, z)$. This is the final axis, for the Cartesian Plane measures our dimensions only in space, namely $3$, and that’s where equations can get a bit more interesting, but when measuring scientific data, we stick with $x$ and $y$.
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