将方程为 的曲线先关于 y 轴进行反射,接着沿 x 轴负方向平移 1 个单位,最后在平行于 y 轴的方向上进行拉伸(缩放因子为 2)。所得曲线的方程由 给出,其中 。
- ((i))
求 。
- ((ii))
在同一幅图中,草拟 和 的图像。
- ((iii))
在不求出 的表达式的情况下,求由曲线 、x 轴以及直线 所围成区域的准确面积。
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完整解法
4((i))
1. Relate $g(x)$ to $f(x)$ by applying the given sequence of transformations.
Let the original curve be .
- Reflection in the -axis: Replace with , giving .
- Translation of unit in the negative -axis (left shift by 1): Replace with , giving .
- Scaling with factor 2 parallel to the -axis: Replace with (or simply multiply the function by ), giving .
Thus, the resulting function is .
2. Use the given equation for $g(x)$ to find the algebraic rule for $f(x)$.
We are given .
Substitute this into our transformation relationship:
To find , we perform a change of variable. Let , which rearranges to .
Substituting gives:
3. Determine the original domain of $f(x)$ corresponding to the transformed domain of $g(x)$.
The domain of is given as .
Apply the same variable substitution to the domain inequalities:
Add to all parts:
Multiply by (and flip the inequality signs):
Replacing with , we obtain the fully defined original function:
for
4((ii))
1. Determine the endpoints, asymptotes, and shape of $y = g(x)$.
Given for :
As , the denominator approaches and , giving a vertical asymptote at .
As , , giving an open endpoint at .
For , and the graph is strictly decreasing, lying entirely in the second quadrant.
2. Determine the corresponding features of the inverse function $y = g^{-1}(x)$.
The graph of is the reflection of across the line .
- The vertical asymptote reflects to a horizontal asymptote .
- The open endpoint reflects to an open endpoint at .
- The resulting graph lies entirely in the fourth quadrant and is strictly decreasing.
3. Sketch both graphs on the same diagram.
- Draw and label the axes and the reference line .
- Sketch in the second quadrant, labeling the vertical asymptote and the open circle at .
- Sketch in the fourth quadrant, labeling the horizontal asymptote and the open circle at .
Both curves should exhibit clear symmetry about the line .
A sketch with in the 2nd quadrant (vertical asymptote , open endpoint ) and in the 4th quadrant (horizontal asymptote , open endpoint ), symmetrical about the line .
4((iii))
1. Find the $x$-coordinate on $g(x)$ that corresponds to the boundary $x=1$ on $g^{-1}(x)$.
Let .
Since the domain of is , we have .
Additionally, as , , which indicates that the -axis boundary ( for ) corresponds to the -axis asymptote boundary ( for ).
2. Relate the required area under $g^{-1}(x)$ to an area involving $g(x)$ using symmetry.
By the symmetry of inverse functions about the line , the region bounded by , the -axis (), and is geometrically identical to the region bounded by (which is ), the -axis (), and .
From the graph of , this is the area enclosed by the rectangle (from to and to ) minus the area under the curve over the same -interval:
3. Evaluate the definite integral of $g(x)$.
Using the standard formula :
4. Calculate the exact final area.
Substitute the evaluated integral back into the area equation:
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