2

Let $p = (0,0)$ and $q = (1,1)$ be two points. I would like to denote the angle between these two points ($45^\circ)$.

I took a look at the lists of symbols, and the symbols $\angle$ and $\measuredangle$ are used to denote angles, but usually when we have $3$ points (a triangle).

Is there any symbol to denote the angle between two points (in relation to the x-axis)?

Would $\measuredangle pq$ be wrong?

user206695
  • 129
  • One way to solve it is to introduce $a = (1, 0)$, but that's not really an answer to your question. – Arthur Apr 15 '15 at 16:22
  • I don't think your question is well posed, ’cause two points don’t determine an angle. If you mean the angle between the line determined by your two points and a horizontal line, then you might use $\arctan m$, where $m$ is the slope of the nonhorizontal line. You know how to denote that, in terms of the coordinates of your points. – Lubin Apr 15 '15 at 16:45
  • Lubin, that's exactly what I need. The angle of the line segment \overline{pq} in relation to an horizontal line. So... $arctan \overline{pq}$ would be right?

    Thanks!

     – user206695 Apr 15 '15 at 17:50

3 Answers3

0

Two points do not determine an angle. You implied x-axis as a standard reference line.

Label or name the three points say $A,B,C$. Then $\measuredangle ABC $ is angle at the middle point B.

Narasimham
  • 40,495
0

There is no symbol to denote the angle that a line defined by $p$ and $q$ makes with the x-axis because that's quite an arbitrary thing. We could measure the angle relative to any other line we want.

Instead, you could specify $X = (1,0)$ then say that $\angle q p X = 45^\circ$ and $\angle p q X = 135^\circ$.

Myridium
  • 2,583
0

In calculus you learn how to represent any point in $(\mathbb R \times \mathbb R) \setminus \{(0,0)\}$ with polar coordinates:

${\displaystyle x=r\cos \varphi }$
$ {\displaystyle y=r\sin \varphi }$

With the complex numbers, you see the same representation:

${\displaystyle z=re^{i\varphi }} $

For more, see Polar coordinate system.

CopyPasteIt
  • 11,366