Calc01_4 - 1.4 Parametric Equations Greg Kelly, Hanford...

1.4 Parametric Equations
Greg Kelly, Hanford High School, Richland, Washington

There are times when we need to describe motion (or a
curve) that is not a function.
We can do this by writing equations for
the x and y coordinates in terms of a
third variable (usually
t
or ).
θ
( 29
x f t =
( 29
y g t =
These are called
parametric equations.
“
t
” is the parameter. (It is also the independent variable)
→

Example 1:
0 x t y t t = = ≥
To graph on the TI-89:
MODE
Graph……. 2
ENTER
PARAMETRIC
Y=
( 29 xt1
t
=
yt1 t =
2nd
T )
ENTER
WINDOW
GRAPH
→

Hit zoom square to see
the correct, undistorted
curve.
We can confirm this algebraically:
x t y t = =
x y =
2
x y = 0 x ≥
2
y x = 0 x ≥
parabolic function
→