The function is defined, for , by .
- (a)
State the period and amplitude of .
- (b)
Sketch the graph of for .

- (c)
On the same diagram in part (b), sketch the graph of .
- (d)
Hence, state the number of solutions, , to the equation
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Worked solution
11(a)
1. Determine the period of the function
The function is . The coefficient of is .
2. Determine the amplitude of the function
The coefficient of the cosine term is .
Period = , Amplitude =
11(b)
1. Determine the maximum and minimum values of the graph
The maximum value of is , so the maximum value of is .
The minimum value of is , so the minimum value of is .
2. Identify the number of cycles and key $x$-coordinates
The period is , so there are two full cycles in the interval .
The key points for the first cycle occur at intervals of : .
3. Sketch the graph
Plot the key points:
Draw a smooth curve through these points.
A sketch of showing two full cycles of an inverted cosine wave starting at , reaching a maximum of at and , a minimum of at and , and crossing the principal axis at .
11(c)
1. Identify the type of graph and find key points to plot
The equation represents a straight line.
When , .
When , .
When , .
When , .
2. Sketch the line on the same diagram
Draw a straight line passing through the points , , , and on the axes from part (b).
A straight line passing through , , , and .
11(d)
1. Rearrange the given equation to match the functions sketched in parts (b) and (c).
2. Relate the rearranged equation to the number of intersections of the graphs.
The equation is now in the form . The number of solutions is the number of points of intersection between the curve and the line for .
3. Determine the number of intersections from the properties of the graphs.
Checking key points:
At , curve , line (curve is above line).
At , curve , line (curve is above line).
At , curve , line . They intersect exactly here.
At , curve , line (line is above curve).
For , the line continues to rise (up to at ) while the curve's maximum is , so they do not intersect again.
Thus, there is exactly point of intersection.
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