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Appendix C C-101<br />

MINI PROJECT 2<br />

Constructing a Parabola<br />

This hands-on mini project shows you how to construct a parabola. Follow the<br />

instructions, and then explain why the curve that you draw is indeed a<br />

parabola. In addition to a sheet of paper and a pen or marker, you’ll need the<br />

following:<br />

• A T-square and a drawing board or surface on which you can easily slide the<br />

T-square left and right in a straight horizontal path<br />

• A piece of string that has the same length as the long bar of the T-square (see<br />

Figure C)<br />

• Two thumb tacks<br />

(Refer to Figure D.) Tack one end of the piece of string to a point on the drawing<br />

board. Call that point F. Tack the other end of the string to the top right<br />

corner of the T-square, as indicated in Figure D. Now, with the pen or marker,<br />

move the T-square horizontally subject to the following two constraints:<br />

The string<br />

Piece of string with<br />

same length as long<br />

bar of T-square<br />

F<br />

T-square<br />

Figure C<br />

Figure D<br />

must be kept taut by the pen, and the pen must stay against the edge of the<br />

T-square. The curve traced out by the pen will be a portion of a parabola. (In<br />

practice, the piece of string that you begin with should actually be just slightly<br />

longer than the length of the T-square, since a slight amount of the string is<br />

taken up in the tacking.)

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