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Sal constructs a line perpendicular to a given line through a point on the line using compass and straightedge. Created by Sal Khan.

Sal constructs a perpendicular bisector to a given line segment using compass and straightedge. Created by Sal Khan.

You can use a protractor or any perfectly circular object. However, many things can be done with a compass that cannot be done with protractor, such as preserving angles and the distances …

Provide the next step in compass and straight-edge constructions of parallel and perpendicular lines.

Step B, it looks like he kind of picked two points and is drawing and using his compass to pivot off of those to kind of draw arcs there. But that's still not clear how it could help.

Now my next step is to find another point on my original line that has the same distance from that point that is off the line. And I can do that by centering my compass on that offline point, and …

Any pair of points can be connected by a line. Connect the pair of black points that makes a line perpendicular to the dashed line segment. The line has two points, point 1 at -5 comma 5 and …

Sal constructs a line that bisects a given angle using compass and straightedge. Created by Sal Khan.

And so in this video we'll see exactly how to draw these magnetic field lines, and how we read them. So to start drawing magnetic field lines the first thing we need to do is to find a direction …