Let two right isosceles triangles be attached by their right vertices. Then GB and EC are congruent and perpendicular.

Drag B or E.

Compare the velocities of B and C.
Compare the velocities of E and G.

AC is the same length as AB rotated 90o. Therefore the velocity of C is the same as the velocity of B rotated 90o. Therefore EC is equal to GB rotated 90o plus a constant vector. To see that the constant vector is zero, let B coincide with A.

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Isosceles right triangles
Figure 9

Alfinio Flores
ASU

This is a prototype of JavaSketchpad, a World-Wide-Web component of The Geometer's Sketchpad. Copyright ©1990-1997 by Key Curriculum Press, Inc. All rights reserved. Portions of this work are being funded by the National Science Foundation (awards DMI 9561674 & 9623018).