home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Trigonometry
/
ProOneSoftware-Trigonometry-Win31.iso
/
trig
/
chapter6.3r
< prev
next >
Wrap
Text File
|
1995-04-09
|
4KB
|
124 lines
122
à 6.3ïParametric Equations
äïPlease draw a graph of the curves described by the given
êêparametric equations.
â
êêêëPlease see Details.
éSïIn earlier sections, we looked at graphs of curves drawn in both
the rectangular coordinate system and the polar coordinate system.ïIn
this section, we will look at drawing graphs a third way.ïThis new ap-
proach involves describing a curve by parametric equations, which are
equations that express the variables x and y in terms of a third varia-
ble or parameter.ïIn this system, the graph is drawn in rectangular
coordinates, and values of the parameter are substituted into the equa-
tions for x and y in order to generate ordered pairs of the form, (x, y).
êêêïIn the figure, you can see a graph of the parame-
êêêtric equations, x = t - 1 and y = t.ïOrdered pairs
êêêare generated by choosing values of t and substitu-
êêêting them into the equations for x and y.ïThe re-
êêêsults for several values of t are shown below.
êêêOrdered pairs of the form (x, y) are then plotted
@fig6301.bmp,10,165
êêêon the rectangular coordinate system to produce the
êêêgraph that you see in the figure.
#êêêê tï│ï-1ï│ï0ï│ï1ï│ï2ï│ï3ï│
#êêêë ─────│──────│─────│─────│─────│─────│
#êêêê xï│è-2 │ -1ï│ï0ï│ï1ï│ï2ï│
#êêêë ─────│──────│─────│─────│─────│─────│
#êêêê yï│è-1 │ï0ï│ï1ï│ï2ï│ï3ï│
êêêè Sometimes it is possible to eliminate the
êêêparameter and express the curve as a function of
êêêjust x and y.ïIn this example, since y = t, you
êêêcan substitute this into the other equation to get,
êêêx = y - 1.ïThis is clearly the equation of a line,
êêêwhich could be graphed to produce the figure.
# 1è Draw a graph of x = t and y = tì, where -2 ≤ t ≤ 2.
@fig6302.bmp,28,225
@fig6303.bmp,28,234
@fig6310.bmp,28,450
üïChoose values of the parameter, t, to generate the chart below.
#êêè tï│ï-2ï│ï-1 │ï0ï│ï1ï│ï2ï│
#êêï─────│──────│─────│─────│─────│─────│
#êêè xï│è-2 │ï-1 │ï0ï│ï1ï│ï2ï│
#êêï─────│──────│─────│─────│─────│─────│
#êêè yï│è4ï│ï1ï│ï0ï│ï1ï│ï4ï│
@fig6303.bmp,3000,3000
è x = têêêêêëEliminate the parameter
#è y = tìêêêêêè x = t, y = tì
#êêêêêêêy = xì
Ç B
2è Draw a graph of x = cos t and y = sin t, where 0 ≤ t ≤ 2π.
@fig6304.bmp,28,225
@fig6305.bmp,28,234
@fig6310.bmp,28,450
üïChoose values of the parameter, t, to generate the chart below.
Use the Key Feature.
#ê tï│è0ï│ π/4 │ π/2 │ 3π/4│ïπï│ 5π/4 │ 3π/2 │ 7π/4 │ 2πï│
#ë ─────│──────│─────│─────│─────│─────│──────│──────│──────│─────│
#ê xï│è1ï│ï.7 │ï0ï│ -.7 │ -1ï│ -.7ï│ï0è│ï.7ï│ï1ï│
#ë ─────│──────│─────│─────│─────│─────│──────│──────│──────│─────│
#ê yï│è0ï│ï.7 │ï1ï│ï.7 │ï0ï│ -.7ï│ -1è│ -.7ï│ï0ï│
@fig6304.bmp,3000,3000
è x = cos têêêêê Eliminate the parameter
è y = sin têêêêê x = cos t, y = sin t
#êêêêêêêxì = cosìt, yì = sinìt
#êêêêêêêxì + yì = 1
Ç A
3ïDraw a graph of x = 1 + cos t and y = sin t, -π/2 ≤ t ≤ π/2.
@fig6306.bmp,28,225
@fig6307.bmp,28,234
@fig6310.bmp,28,450
üïChoose values of the parameter, t, to generate the chart below.
Use the Key Feature.
#ê tï│ -π/2 │-π/3 │-π/6 │ï0ï│ π/6 │ïπ/3 │ïπ/2 │
#ë ─────│──────│─────│─────│─────│─────│──────│──────│
#ê xï│è1ï│ 3/2 │ 1.9 │ï2ï│ 1.9 │ï3/2 │ï1è│
#ë ─────│──────│─────│─────│─────│─────│──────│──────│
#ê yï│ï-1ï│ -.9 │ -.5 │ï0ï│ï.5 │ï.9ï│ï1è│
@fig6306.bmp,3000,3000
è x = 1 + cos têêêêèEliminate the parameter
è y = sin têêêêêx = 1 + cos t, y = sin t
#êêêêêêë (x - 1)ì = cosìt,
#êêêêêêë yì = sinìt
#êêêêêêë (x - 1)ì + yì = 1ïNote
êêêêêêë that 1 ≤ x ≤ 2.
Ç A
4è Draw a graph of x = 2∙cos t and y = 3∙sin t.
@fig6308.bmp,28,225
@fig6309.bmp,28,234
@fig6310.bmp,28,450
üïChoose values of the parameter, t, to generate the chart below.
Use the Key Feature.
#ê tï│è0ï│ π/4 │ π/2 │ 3π/4│ïπï│ 5π/4 │ 3π/2 │ 7π/4 │ 2πï│
#ë ─────│──────│─────│─────│─────│─────│──────│──────│──────│─────│
#ê xï│è2ï│ 1.4 │ï0ï│ 1.4 │ -2ï│ -1.4 │ï0è│ -1.4 │ï2ï│
#ë ─────│──────│─────│─────│─────│─────│──────│──────│──────│─────│
#ê yï│è0ï│ 2.1 │ï3ï│ 2.1 │ï0ï│ -2.1 │ -3è│ -2.1 │ï0ï│
@fig6309.bmp,3000,3000
è x = 2∙cos têêêêë Eliminate the parameter
è y = 3∙sin têêêêë x = 2∙cos t, y = 3∙sin t
êêêêêêêx/2 = cos t, y/3 = sin t
#êêêêêêêxì/4 = cosìt
#êêêêêêêyì/9 = sinìt
#êêêêêêêxì/4 + yì/9 = 1
Ç B