It is given that , where .
- (i)
Sketch the graph of , showing clearly the coordinates of the turning points and the equation(s) of any asymptote(s).
- (ii)
By inserting a suitable graph to your sketch in (i), find the set of values of , in terms of , for which the equation has two distinct positive roots.
- (iii)
The curve undergoes the transformations , and in succession:
: A translation of units in the direction of -axis,
: A stretch parallel to the -axis with scale factor of , and
: A translation of units in the direction of -axis.
Given that the resulting curve is , find the value of .
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Worked solution
9(i)
1. Identify the vertical and oblique asymptotes of the graph.
For , the fraction is undefined when the denominator is zero.
As , , so the vertical asymptote is .
As , , so the curve approaches the line .
The oblique asymptote is .
2. Find the $x$-coordinates of the turning points by differentiating.
To find the turning points, set :
Since , taking the square root gives:
3. Calculate the corresponding $y$-coordinates of the turning points.
Substitute back into the original equation to find :
When :
When :
The turning points are and .
4. Deduce the sketch properties using the given condition $0 < m < 1$.
Since , we have and .
This means the local maximum lies in the first quadrant, to the left of the asymptote .
The local minimum lies to the right of .
The -intercept is at (which is negative).
With these features, sketch the two branches bounded by and .
Asymptotes: and
Turning points: [local maximum] and [local minimum]
(The sketch should show a rational curve with two branches separated by the vertical asymptote , bounded by the oblique asymptote . Since , the local maximum is strictly in the first quadrant.)
9(ii)
1. Manipulate the given equation to relate it to the function $\mathrm{f}(x)$.
Dividing by since is an asymptote and not a root:
The roots of the equation correspond to the -coordinates of the intersection points between the curve and the horizontal line .
2. State the key features of the graph of $y = \mathrm{f}(x)$ derived from part (i).
From part (i), setting gives and .
The local maximum point is .
The local minimum point is .
The -intercept is found by setting :
3. Determine the values of $k$ that give two positive roots on the left branch of the curve.
For the equation to have two distinct positive roots, the line must intersect the curve at two distinct points where .
On the left branch (), the curve crosses the -axis at , rises to the maximum at , and then falls towards the vertical asymptote .
To intersect this branch at two points with , the horizontal line must lie strictly above the -intercept and below the maximum.
Thus, we require:
4. Determine the values of $k$ that give two positive roots on the right branch of the curve and combine the results.
The right branch of the curve () lies entirely in the region where is positive. It has a local minimum at .
Any horizontal line strictly above this minimum will intersect the right branch at two distinct points, both of which will have .
Thus, we also have valid solutions when:
Combining these, the complete set of values is .
9(iii)
1. Apply transformation $A$ to the original curve equation.
Transformation is a translation of units in the -direction, which means replacing with .
2. Apply transformations $B$ and $C$ to find the final equation.
Transformation is a stretch parallel to the -axis with scale factor , which requires replacing with .
Transformation is a translation of units in the -direction, which means subtracting from the entire function.
3. Compare the transformed equation with the given resulting equation to solve for $m$.
We are given that the resulting curve is . By comparing the terms with our deduced equation:
Taking the square root:
Since we are given in the question stem, we reject the negative root to obtain:
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