Guide
Desmos Geometry Tool: Circles and polygons
Learn how to create accessible geometry shapes and how to measure angles using the Desmos Geometry Tool!
The first two posts in the Math Shapes series featured hands-on activities to build shape concepts. The Math shapes: Marshmallows and toothpicks activities post introduced tracing shapes and creating simple shapes using marshmallows and toothpicks. The Math shapes: Classifying and drawing shapes discussed organizing common shapes by classifications: polygons, triangles and quadrilaterals and then typical tools used by BLV students to create and/or draw the shapes. Since most classroom math teachers and many TSVIs have vision, let’s first introduce the Desmos Geometry Tool first without a screen reader and then in separate posts, learn how to use the tool with a screen reader. The first Desmos Geometry Tool post, Desmos Geometry Tools: Points and lines, introduced the Desmos Geometry Tool and how teachers/students with vision can create digital points and different types of lines without a screen reader. This post will focus on how sighted teachers and students can use the Desmos Geometry Tool to create shapes and measure angles.
Getting started with Desmos geometry shapes
Go to Desmos.com and select the Geometry button or go directly to desmos.com/geometry.
Create a free account and log in. Must be signed in to save or share a creation with a student.
Confirm that the grid lines and axis numbers are on the canvas.
- To turn the grid and axis numbers on, go to the Settings button options (wrench icon on far right of the tool bar) and toggle the Grid on and select the Axis > Axis numbers.
Terms
- Radius: The radius of a circle is the distance between the center of the circle and the point on the circle’s edge. Radius is half of the diameter.
- Diameter: The line that passes through the center and meets the circumference at opposite ends. It is twice as long as the radius of the circle.
- Angle: An angle is a combination of two rays or lines that shares a common endpoint. The two rays are called the sides of an angle, and the common endpoint is called the vertex.
- Arc: An arc is any portion (other than the entire curve) of the circumference of a circle.
- Minor arc: An arc whose measure is less than 180 degrees
- Major arc: An arch whose measure is greater than 180 degrees
- Semicircle: An arc whose measure equals 180 degrees; it divides the circle in two
Tool bar buttons
Tool bar above the canvas has the following tool buttons in order. The previous post introduced the Select, Point and Line tool buttons. This post focuses on the Circle, Measure an Angle and Polygon tool buttons.
- Select tool button
- Point tool button
- Line tool button
- Circle tool button
- Measure an Angle tool button
- Polygon tool button
Circle tool button
Select the Circle tool options and the popup menu has Circle, Compass and Arc. To stop or exit a creating mode, click on the Select tool button.
- Circle: To create a circle, select the Circle tool button, then in the drop down menu, select the Circle option. In the canvas, click on the desired location to make the point in the center of the circle. Move your cursor out which creates the circle (around the center point). Click again when the circle is the desired size. This also creates a point on the circle. Click on the Select tool button to exit the Circle creation mode.
- Once the circle is created, you can increase or decrease the circle size by dragging the first point (center point). The second point on the edge of the circle does not move.Another option is to change the size of the circle by dragging the second point which is on the edge of the circle.To add a radius to the circle, select the Line tool button options then Segment. Click on the center point, then click on the point on the edge of the circle.To adjust the radius (which also adjusts the size of the circle), move the point on the edge of the circle.To add text or change the color, click on a point and the tool bar changes. Select the Styles button (three dots) to open the Styles menu. Select Label and type in the desired label.Note: You can create a segment first, then add the circle to the segment’s two points.
- To create a circle with a diameter: Create a line segment. Add a midpoint by selecting the Point tool option, then selecting the Midpoint). Create a circle with the center at the midpoint.
- Measure an Angle tool: The Measure an Angle tool has two options: Angle and Directed Angle.
- Angle: First, create a circle with 2 line segments, each starting from the center and going to a point on the outside edge. Label the angle: Example: Label the center point C (for Center) and the outer points D and E. Select the Measure an Angle tool options, then Angle. Now click an outside point on the edge, the center point, then the next outside point on the edge. (In this case, Point D, Point C (center) and then Point E.) The measurement number now appears by Point C.
- Directed Angle: Create a circle with C for the center point and two line segments D and E for the point on the outer edge. Select the Measure an Angle tool options, then Directed Angle. Click on the outer point that is to the right of the second line segment. Then click on the center point and finally click on the second outer point. The number of degrees now appears by the center, along with a directional arrow from the first segment up to the second segment. If you move the top point below the first point, the directional arrow changes directions (now points down instead of up) and the degrees begin measuring the negative, smaller section of the angle from the original first segment down (clockwise) to the second segment (instead of measuring the larger outside portion of the angle). Trigonometry requires positive and negative rotation.
- Arc: Place three points on the outer edge of the circle. Click on the Select tool button, then click on the outer edge of the circle anywhere between the three points. This makes the outer edge of the circle between the three points slightly darker in color and that portion of the outer edge is now an “arc”. To make this easier to see, change the color of the arc. You can make a major or minor arc.
- Polygon tool button: Creates various shapes.
- To make a triangle: Select the Polygon tool then make three points on the canvas. To finish with the triangle, create the three points and then click on the first point again.
- The center of the polygon is shaded in. Each point in the polygon is called a vertex. Any vertex can be manipulated, changing the size or shape of the triangle. The triangle can be customized by adding labels, changing the color of the vertices and/or the color of the shaded center. Click on a vertex or the center, then select Style tool button (three dots) to customize the triangle. Uncheck the “Draggable” box under the Style tool button to make a vertex locked in place, stopping the vertex from being manipulated/moved. Angle measurements can be added using the Measure an Angle tool.
- To make other polygons: Repeat the steps for creating a triangle, except make four or more points on the canvas.
- To make a triangle: Select the Polygon tool then make three points on the canvas. To finish with the triangle, create the three points and then click on the first point again.
Resources
More posts in this geometry series!
- Math shapes: Marshmallows and toothpicks activity!
- Math shapes: Classification and drawing of shapes
- Math shapes: Introducing APH Memory Puzzles
- Desmos Geometry Tool: Points and lines
- Desmos Geometry Tool: Circles and polygons
- Creating an accessible geometry worksheet: Desmos Geometry Tool (workflow)
- More Desmos Geometry Tool posts! (Coming soon!)
By Diane Brauner
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