If the given point is above the line, you should draw this arc below the line. If the given point is below the line, you should draw this arc above the line. The arc does not have to be very long, as long as part of it falls directly under the given point.

Remember, a perpendicular line is a line that creates a 90 degree angle.

If the line and point are not already labeled, you might want to label them to easily keep track of the steps. For example, you might have line m{\displaystyle m} and point A{\displaystyle A}.

It does not matter how wide you set the compass, as long as it can intersect the given line. Make sure the arc reaches above the given point and intersects the given line. For example, you should set the compass tip at point A{\displaystyle A} and create an arc that intersects line m{\displaystyle m} at point B{\displaystyle B}.

The arc only has to be long enough to show where it intersects the given line. For example, you should set the compass tip at point B{\displaystyle B} and create an arc that intersects line m{\displaystyle m} at point C{\displaystyle C}.

The arc only has to be long enough to show where it intersects the first arc. For example, you should set the compass tip at point C{\displaystyle C} and create an arc that intersects the first arc at point D{\displaystyle D}.

For example, a line drawn through point A{\displaystyle A} and point D{\displaystyle D} will be parallel to line m{\displaystyle m}.

If the line and point are not already labeled, you might want to label them to easily keep track of the steps. For example, you might have line m{\displaystyle m} and point A{\displaystyle A}.

Ensure that the transverse line extends well beyond the given point. For example, you might draw a line through point A{\displaystyle A} that intersects line m{\displaystyle m} at point B{\displaystyle B}. The new line segment would be AB{\displaystyle AB}.

The exact width of the compass does not matter, as long as it is less than half the width of the line segment. For example, you should set the width of the compass so that it is less than half the width of line segment AB{\displaystyle AB}.

For example, you should set the compass at point B{\displaystyle B} and draw an arc that intersects line segment AB{\displaystyle AB} at point C{\displaystyle C} and line m{\displaystyle m} at point D{\displaystyle D}. This creates the angle CBD{\displaystyle CBD}.

For example, you should set the compass at point A{\displaystyle A} and draw an arc that intersects the transverse line above point A{\displaystyle A} at point P{\displaystyle P}.

For example, the first angle you created was CBD{\displaystyle CBD}, so set the tip of your compass on point D{\displaystyle D} extend it to point C{\displaystyle C}.

For example, you should set the compass tip at point P{\displaystyle P} and draw an arc that intersects the previous arc at point Q{\displaystyle Q}. This gives you angle PAQ{\displaystyle PAQ}, which corresponds to angle CBD{\displaystyle CBD}.

For example, a line drawing through point A{\displaystyle A} and point Q{\displaystyle Q} creates line f{\displaystyle f}, which is parallel to line m{\displaystyle m}.