The diagram shows part of the graph of y=atan⁡(bx+c)y = a\tan(bx + c). The graph has vertical asymptotes at x=−4πx = -4\pi and x=4πx = 4\pi and passes through the points P and Q.

  1. (i)

    Explain why b=18b = \tfrac{1}{8}.

  2. (ii)

    Hence find the equation of the curve.

  3. (4)
    1. (b)

      The function f(x)f(x) is defined by f(x)=4+3sin⁡2xf(x)=4+3\sin 2x for 0∘≤x≤360∘0^\circ \le x \le 360^\circ. Sketch the graph of y=f(x)y=f(x) on the axes below.

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Worked solution

4(a)(i)

1. Determine the period of the tangent graph from the given asymptotes

The distance between consecutive vertical asymptotes gives the period of the tangent graph.
Period=4π−(−4π)=8π\text{Period} = 4\pi - (-4\pi) = 8\pi

2. Relate the period to the parameter $b$ and solve for $b$

The period of y=atan⁡(bx+c)y = a\tan(bx + c) is given by πb\frac{\pi}{b}.
πb=8π\frac{\pi}{b} = 8\pi
b=π8π=18b = \frac{\pi}{8\pi} = \frac{1}{8}

Answer

The period of the graph is 8π8\pi, and since the period of y=atan⁡(bx+c)y = a\tan(bx + c) is πb\frac{\pi}{b}, we have πb=8π\frac{\pi}{b} = 8\pi, which gives b=18b = \frac{1}{8}.

4(a)(4)(b)

1. Determine the amplitude, period, and vertical shift of the function

For y=4+3sin⁡2xy = 4 + 3\sin 2x:

  • Amplitude =3= 3
  • Vertical shift =4= 4 (principal axis is y=4y = 4)
  • Period =360∘2=180∘= \frac{360^\circ}{2} = 180^\circ

2. Identify the key coordinates and sketch the graph for $0^\circ \le x \le 360^\circ$

Since the period is 180∘180^\circ, there are two full cycles in the domain 0∘≤x≤360∘0^\circ \le x \le 360^\circ.
Maximum value =4+3=7= 4 + 3 = 7
Minimum value =4−3=1= 4 - 3 = 1
Key points for the first cycle:

  • Start: (0∘,4)(0^\circ, 4)
  • Max: (45∘,7)(45^\circ, 7)
  • Axis crossing: (90∘,4)(90^\circ, 4)
  • Min: (135∘,1)(135^\circ, 1)
  • End of cycle 1: (180∘,4)(180^\circ, 4)
    Key points for the second cycle:
  • Max: (225∘,7)(225^\circ, 7)
  • Axis crossing: (270∘,4)(270^\circ, 4)
  • Min: (315∘,1)(315^\circ, 1)
  • End of cycle 2: (360∘,4)(360^\circ, 4)
    Draw a smooth continuous curve through these points.
Answer

A smooth sine curve starting at (0∘,4)(0^\circ, 4), reaching a maximum of 77 at 45∘45^\circ and 225∘225^\circ, a minimum of 11 at 135∘135^\circ and 315∘315^\circ, and completing two full cycles to end at (360∘,4)(360^\circ, 4).

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