Parametric Graphing (TI 85)

Goal: We wish to graph parametric equations given by x=f(t) and y=g(t).

Preliminaries: Choose MODE and select Param. Exit to the home screen.

Step by step method:

• Choose GRAPH and then E(t)= (this is F1). Fill in the formula for f(x) as xt1 and the formula for g(t) as yt1.
• Choose the WINDOW menu (from F2) and fill in the intervals for x, y, and t. The intervals for x and y determine the portion of the coordinate plane that is viewed. The interval for t determines (along with the formulas for f(t) and g(t)) the points which get plotted.
• Press GRAPH (F5).

Remarks: The choice of the interval for t is important. If one function is given by x=t then it would be appropriate to choose the same interval for t as for x. A similar choice applies if one formula is y=t.

The tStep value must be selected with care since the consequent x and y steps will often be irregular since the value of t is processed through f and g. Very small values of t will result in very slow plotting while very large values will result in a "chunky" curve or even downright incorrect results.

M132 Home