Question 6.5.1: Graphing y = a tan b(x - c) or y = a cot b(x - c) OBJECTIVE ...
Graphing y = a tan b(x – c) or y = a cot b(x – c)
OBJECTIVE
Graph a function of the form y = a tan [b(x – c)] or y = a cot [b(x – c)], where b > 0, by finding the period and phase shift.
Step 1 Find the following:
vertical stretch factor = |a|
period = \frac{\pi}{b}
phase shift = c
Step 2 Locate two adjacent vertical asymptotes.
For y = a tan [b(x – c)] solve:
b(x – c) = -\frac{\pi}{2} and b(x – c) = \frac{\pi}{2}.
For y = a cot [b(x – c)] solve:
b(x – c) = 0 and b(x – c) = π.
Step 3 Divide the interval on the x-axis between the two vertical asymptotes into four equal parts, each of length \frac{1}{4}(\frac{\pi}{b}).
Step 4 Evaluate the function at the three x values found in Step 3 that are the division points of the interval.
Step 5 Sketch the vertical asymptotes using the values found in Step 2.Connect the points in Step 4 with a smooth curve in the standard shape of a cycle for the given function. Repeat the graph to the left and right over intervals of length \frac{\pi}{b}.
Graph y=3 \tan \left[2\left(x-\frac{\pi}{4}\right)\right].
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1.
\begin{aligned}&y= \underset{\overset{\uparrow }{a=3}}{3} \tan \left[ \underset{\overset{\uparrow }{b=2}}{2}\left(x-\underset{\overset{\uparrow }{c=\frac{\pi}{4}}}{\frac{\pi}{4}}\right)\right] \end{aligned}
vertical stretch factor = |a| = |3| = 3
\text { period }=\frac{\pi}{b}=\frac{\pi}{2} \text { phase shift }=c=\frac{\pi}{4}
2.
and
\begin {array} {rl|rl} \begin{aligned}2\left(x-\frac{\pi}{4}\right) &=-\frac{\pi}{2} \\x-\frac{\pi}{4} &=-\frac{\pi}{4} \\x &=-\frac{\pi}{4}+\frac{\pi}{4} \\x &=0\end{aligned}&& \begin{aligned}2\left(x-\frac{\pi}{4}\right) &=\frac{\pi}{2} \\x-\frac{\pi}{4} &=\frac{\pi}{4} \\x &=\frac{\pi}{4}+\frac{\pi}{4} \\x &=\frac{\pi}{2}\end{aligned}\end {array}
3. The interval \left(0, \frac{\pi}{2}\right) \text { has length } \frac{\pi}{2} \text {, and } \frac{1}{4}\left(\frac{\pi}{2}\right)=\frac{\pi}{8} \text {. }
The division points of the interval \left(0, \frac{\pi}{2}\right) are 0+\frac{\pi}{8}=\frac{\pi}{8}, 0+2\left(\frac{\pi}{8}\right)=\frac{\pi}{4} \text {, and } 0+3\left(\frac{\pi}{8}\right)=\frac{3 \pi}{8}.
4.
\begin{array}{|c|c|}\hline x & y=3 \tan \left[2\left(x-\frac{\pi}{4}\right)\right] \\\hline \frac{\pi}{8} & -3 \\\hline \frac{\pi}{4} & 0 \\\hline \frac{3 \pi}{8} & 3 \\\hline\end{array}
5.
