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We click on the slider icon. Click somewhere up here. The slider dialog box opens and we
can choose number or angle. If we choose angle, we automatically get degrees. If we choose
number and go from 0 to 360, we must then add degrees when we define the angle. So here
we are going to chose angle and see that degrees are there. GeoGebra automatically names it
alpha. If we want it to name it something else, we use the dropdown menu or type whatever
we want. Let’s say that we want our slider to go from 0 to 180 degrees. You cannot erase
the degree sign. You must have 180 degrees. If you accidently erase the degree sign, just
hit enter and it will revert to 360 degrees and you can try it again. Now I have found
that the width of the slider must be a multiple of the interval length. Just for the fun of
it, we are going to put 90 here and click on apply. We will see that the slider will
give only the even numbered angles easily. See. So now right-click on the slider, choose
properties and make the length of the slider 180. Now we will be able to get all of the
angles from 0 to 180 degrees easily. We will leave it at 60 degrees. Now we want an angle
that matches the slider. We don’t want the Angle with 3 point tool so we click on the
little arrow to get to the Angle with given size tool. Now we need to put in 2 points
which will form the base of the angle. The first point is the right point, then comes
the vertex and then it will ask us what size we want. We delete the 45. Remember because
alpha already has degrees, we do not have to worry about degrees here. So we click on
alpha. See the 60 there. Let’s check it. Click on the move icon, slide the slider and
see that the angle changes. Let’s put rays in. We can put rays in or line segments depending
on where you live. We are going to put in rays. Click on the vertex and then other point.
Click on the vertex again. Make sure the points glow before you click and now click on other
point. Now we don’t really want to see these points, but we cannot delete them. We can
only hide them. So right-click and deselect “show object”. Don’t delete, right-click
and deselect “show object”.