Sketchpad Investigations
Thursday, July 13, 1995
We began the morning with an investigation of features of the version 3.0 of the Geometer's Sketchpad.
1. Annie gave us the following exercise:
 Open a new Sketchpad window and create x and y axes.
 Create three points, A, B, and X on the x axis, and
find their coordinates.
 Using the calculator, calculate the x coordinate of each
(hereafter these coordinates will be called simply
X, A, and B).
2
 The equation to plot is F(X) = AX + B
2
 Using the calculator, calculate AX + B
 Select X and this equation and, using the calculator,
plot x,y (graph menu).
 Move X along the x axis until the point x,y appears
on the screen.
 Find the locus of x,y as X moves along the x axis:
 Select X, the x axis, and x,y and construct
the locus (Construct menu).
 Move A and B and describe the results.
PARABOLA!
2. Next we looked at a geometric representation:
 draw line segment AB
 put a point C somewhere not on it (slightly above)
 construct a point X on the line and connect C and X
 select line CX and construct its perpendicular bisector
 select line CX and trace locus
 make an Animate button
 Question: How do you find the point on the perpendicular
bisector of CX that is on the parabola?
PARABOLA!
