Arrow slider – GeoGebra QuickieLinda Fahlberg-Stojanovska

Angle Slider with GeoGebra

Goal: Create a angle slider and a corresponding anglethat changes with the slider

Angle sliders in action: Triangle Angle-Side-Angle

What you see / What you have

Notes:

There are 2 angles – the 1st is the angle α which is defined as a slider.

The 2ndangle is the angle βdefined as the angle through point A, then B (makes B the vertex) and size α.

In this way change the value of the slider α automatically changes the size of β.

Defining β this way defines both β and the point A’, that is, we do not define A’ separately.

In order that the user is not confused by the 2 angles, we simply “label” β by value (image at left) and do not include it’s name (image at right).

Step-by-Step Directions

  1. Select the Slidertool and click in the upper left-hand corner of the Drawing pad. A dialog box will open.
  2. Select Angle (instead of Number).
  3. Click in the max field and carefully erase the 360, but NOT the degree sign and type in 180. (If you accidently erase the degree sign you can use the keyboard shortcut Crtl+Shift+O or you can cancel and start over.)
  4. Click on the Slider tab and in the Width field, type in 180. (This will make it possible to slide through every angle.)
  5. Click on Apply.
  6. Click and drag the slider to something visible - for example to 30°.
  7. Select the New point tool and click once towards the bottom middle of the Drawing pad and again to the left – but not too far left – to get 2 points A and B.
  8. Select the Angle with Given Size tool from the Angle tools menu and then click on point A and then on point B. (They will glow when you have them selected.) A dialog box will open. Erase the 45° and click on α at right.Click on OK.
    Notice both the angle β and the point A’ are created. The points A and A’ are equally distant from B because they lie on the same circle. (If you don’t see A’ , using the Move tool, click and drag point B closer to point A.)
  9. Select the Ray tool from the Line tools menu and click on B and then on A for bottom ray aand then again on B and then on A’ for top rayb.

Everything else is decoration.

  1. Right-click on any object and choose Properties from the drop-down menu. One-by-one change the properties of all of the objects we have created to what you want.

On the Basics tab:

  • On the angle α, check that both “Name & Value” are selected.
  • On the angle β, click on the down arrow by “Show Label” and select “Value”.
  • On the points A and A’, deselect “Show object”.
  • On the point B and the rays a and b, deselect “Show label” .

On the Color tab:

  • On the angle α, chose a color you like. Then, click on angle β and choose the same color. (This connects these angles in the eye of the user.)

On the Style tab:

  • On the angle α, increase the line thickness to 4.
  • On the angle β, increase the size to 60. (Then you can use the Move tool to position the angle label, but we suggest you slide the slider to both ends before choosing position.)

July 20091