What is the first step in constructing a 90-degree angle using a compass?

To construct a 90-degree angle using a compass, the first step is to draw one large arc with the needle on the line. This action is fundamental because it enables you to create two intersections with the line, which will subsequently allow you to establish a perpendicular bisector.

When you place the compass at a point on the line and draw an arc, you create two points of intersection on either side of the line. These intersections will be used to draw another line that bisects the initial line segment, forming a right angle (90 degrees) with it. This method is rooted in the geometric principles of circle geometry, where the arcs can be used to ensure accurate angles are created.

Initiating the construction with this arc is essential, as it lays the groundwork for the process of using the compass to find the necessary points that will define the right angle. Other steps, such as drawing a straight line segment or marking the midpoint, come later in the process. Using a protractor isn't necessary here, as the compass and straightedge method is a more traditional geometric construction technique that emphasizes understanding angles and their relationships.