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
→
