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2.1 Lines, Circles, Rectangles, Arcs, Polygons & Rays

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Autodesk Certified User ACU

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1 Introduction & Exam Foundations

1.1 Current Exam Facts 1.2 Candidate Profile, UI & Help 1.3 Inquiry Commands & Draw Order

2 Chapter 2: Basic Drawing Objects

2.1 Lines, Circles, Rectangles, Arcs, Polygons & Rays 2.2 2D Isometric Drawings

3 Chapter 3: Polylines

3.1 Drawing Open & Closed Polylines 3.2 Editing & Joining Polylines

4 Chapter 4: Selection Sets & Layers

4.1 Creating & Refining Selection Sets 4.2 Managing Layers

5 Chapter 5: Blocks

5.1 Creating Basic Blocks 5.2 Inserting & Modifying Block Instances 5.3 Transferring Content Between Drawings

6 Chapter 6: Draw with Accuracy

6.1 Object Snaps & Object Snap Tracking 6.2 Absolute, Relative & Polar Coordinates 6.3 Dynamic Input & Direct Distance Entry

7 Chapter 7: Properties & Transform Edits

7.1 Object Properties & Match Properties 7.2 Move, Copy, Rotate, Mirror, Scale & Stretch 7.3 Grip Editing

8 Chapter 8: Trim, Arrays, Offset & Corners

8.1 Trim, Extend & Lengthen 8.2 Rectangular & Polar Arrays 8.3 Offsetting Objects 8.4 Fillet & Chamfer

9 Chapter 9: Text & Leaders

9.1 Single-Line & Multiline Text 9.2 Leaders & Multileaders

10 Chapter 10: Dimensions

10.1 Linear, Aligned, Angular, Radius & Diameter Dimensions 10.2 Continue & Baseline Dimension Strings 10.3 Dimension Styles

11 Chapter 11: Hatch, Layouts & Printing

11.1 Hatches & Fill Patterns 11.2 Layouts & Viewports 11.3 Viewport Scale & Title Blocks 11.4 Plotting & Page Setup Manager

2.1 Lines, Circles, Rectangles, Arcs, Polygons & Rays

Key Takeaways Explain This Topic AI

LINE draws connected straight segments as separate objects; the Close option snaps the last segment back to the very first point picked

CIRCLE defaults to Center, Radius but also supports Diameter, 2-Point, 3-Point, and two Tangent-Tangent variations for fitting a circle between existing objects

RECTANG lets you set Chamfer, Fillet, or Width before you pick corners, and it always draws a single closed polyline object

ARC defaults to a three-point pick, but AutoCAD assumes a counterclockwise sweep from the start point unless you explicitly choose a method that lets you specify direction or angle

POLYGON's Inscribed option fits the shape inside a circle of the radius you give (vertices touch the circle), while Circumscribed fits it outside (edges are tangent to the circle) — the two produce different-sized polygons for the same radius

Last updated: August 2026

Building the Basic Object Set

Every AutoCAD drawing is assembled from a small set of primitive objects. The ACU AutoCAD exam expects you to know not just that these commands exist, but which option prompt controls size, shape, and orientation — because that is where most real-world (and exam) mistakes happen.

LINE

The LINE command draws one or more straight segments, but each segment is stored as its own independent object (unlike a polyline, covered in the next chapter). After you pick a start point and at least one more point, the command keeps prompting for additional points until you press Enter, Escape, or use one of two special responses:

Close — available once you've drawn at least two segments; it draws a final segment back to the very first point you picked and ends the command. This is the fastest way to close a triangle or irregular shape without snapping to the start point manually.

Undo — backs up one segment at a time without leaving the command, useful when a pick point is wrong but you want to keep drawing.

Common trap: Because LINE segments are separate objects, selecting "one side" of a shape drawn with LINE only selects that single segment — not the whole outline. If a question describes needing to move, offset, or fillet an entire multi-segment outline as one object, that is a signal for PLINE , not LINE.

CIRCLE

The default CIRCLE workflow is Center, Radius — pick a center point, then type or pick a radius. But the command exposes several other construction methods, each solving a different real-world layout problem:

  • Option How it works When you'd use it
  • Center, Radius (default) Pick center, type/pick radius You know the center and radius
  • Center, Diameter Pick center, type/pick diameter You know the center and overall diameter (e.g., pipe OD)

2-Point Pick two points that define the diameter You know two points the circle must pass through, opposite each other

3-Point Pick three points on the circumference You know three points the circle must pass through

Tan, Tan, Radius (TTR) Pick two objects to be tangent to, then give a radius Fitting a fillet-like circle between two lines or circles

Tan, Tan, Tan Pick three objects to be tangent to Inscribing a circle exactly touching three edges

Common trap: Mixing up radius and diameter. If a problem states a 10" diameter hole, typing "10" at a default Center-Radius prompt produces a 20"-diameter circle. Always confirm which value the prompt is asking for, or explicitly invoke the Diameter option.

RECTANG

RECTANG draws a rectangle as a single closed polyline object from two diagonal corner picks. Before picking the first corner, you can set modifying options that persist for subsequent rectangles until changed:

  • Chamfer — cuts angled corners of a specified distance (or two distances)
  • Fillet — rounds all four corners to a specified radius
  • Width — sets a uniform line width for the polyline's segments
  • Elevation / Thickness — 3D properties, rarely tested at ACU level

Area and Rotation — alternate ways to size and orient the rectangle instead of picking a second corner directly

Common trap: Chamfer and Fillet settings stick between rectangles. If a previous rectangle used a 0.5" fillet, the next RECTANG will silently apply that same fillet unless you reset it to zero.

ARC

ARC is the most option-heavy basic shape command. The default invocation (just clicking three points) uses 3-Point , but the full option set — accessed by starting with a letter option or via the ribbon's Arc gallery — includes combinations of Start, Center, End, Angle, Direction, Radius, and Length of Chord:

3-Point — pick a start, a point on the arc, and an end point

Start, Center, End — pick start, then center, then an end angle (radius is implied by the start-to-center distance)

  • Start, Center, Angle — like above, but you type an included angle instead of picking an end
  • Start, Center, Length — you specify the chord length instead of an angle
  • Start, End, Radius — useful when you know two endpoints and a radius but not the center

Start, End, Angle or Start, End, Direction — useful when the arc must leave the start point tangent to something

Center, Start, End — same geometry as Start-Center-End, entered in a different order

Common trap: AutoCAD always sweeps arcs counterclockwise from the start point by default. If you pick a start and end point expecting a short arc but get the long way around the circle instead, you likely need to swap your point order or specify a negative angle — the software isn't broken, it's following the CCW convention.

POLYGON

POLYGON draws a regular polygon (3 to 1024 equal sides) as a single closed polyline. After specifying the number of sides and a center point, you choose one of two fitting methods:

Inscribed in circle — you specify a radius, and the polygon's vertices sit exactly on a circle of that radius (the polygon is smaller than the circle)

Circumscribed about circle — you specify a radius, and the polygon's edge midpoints are tangent to a circle of that radius (the polygon is larger than the circle)

Alternatively, the Edge option skips the center/radius approach entirely — you specify two points that define one edge, and AutoCAD builds the rest of the polygon from that edge length and orientation.

Common trap: For an identical radius value, Inscribed and Circumscribed do not produce the same-size polygon. Circumscribed always produces a larger polygon than Inscribed for the same radius, because the radius is measured to different reference points (vertex vs. edge midpoint).

RAY and XLINE (Construction Line)

When you need infinite reference geometry for aligning other objects rather than a finished, plottable shape, AutoCAD provides two dedicated tools:

  • RAY — starts at a specified point and extends to infinity in one direction only
  • XLINE (Construction Line) — passes through a specified point and extends to infinity in both directions

Both are commonly used as temporary layout aids (e.g., projecting alignment points between views) and are typically placed on a dedicated non-plotting or construction layer, then erased once they've served their purpose. Because they have no defined endpoints, standard length-based editing (like LENGTHEN) doesn't apply to them the way it does to lines and arcs.