[在此问题中,所给图像的草图未按比例绘制] 和 的图像如下所示。 在不同的图上,分别画出下列函数的图像草图, 写出所有渐近线方程以及与坐标轴交点的坐标。
- (a)
,
- (b)
,
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完整解法
1(a)
1. Identify the transformation from $y^2 = \mathrm{f}(x)$ to $y^2 = \mathrm{f}(-2x)$.
The equation replaces with . This corresponds to a horizontal scaling by a factor of and a reflection in the -axis.
2. Determine the new asymptote and $x$-intercept.
Applying the transformation to the key features of :
- Vertical asymptote:
- -intercept (vertex): , giving the coordinate
3. Determine the shape and domain of the new graph.
The original graph exists for and opens to the left from .
For the transformed graph, the domain is .
The new graph consists of two branches starting at and opening to the right towards the vertical asymptote , maintaining symmetry about the -axis.
Sketch of :
- A curve symmetric about the -axis consisting of two branches.
- The vertex (-intercept) is at .
- The curve opens to the right from the vertex.
- There is a vertical asymptote at , which the branches approach as .
- No -intercepts.
1(b)
1. Determine the intervals where $\mathrm{f}(x)$ is positive or negative from the $y^2 = \mathrm{f}(x)$ graph.
The relation only yields real values of when .
Given that the graph of consists of branches starting at and opening to the left towards the asymptote , this curve only exists for .
Furthermore, it is explicitly defined "only for ", ruling out any regions .
Therefore, we deduce:
- for
- for and
2. Relate $y = \mathrm{f}(x)$ to the provided graph of $y = |\mathrm{f}(x)|$.
Using the signs of , we construct from :
- For : Since , . The sketch of in this region is identical to the graph of .
- For and : Since , . The sketch is obtained by reflecting the corresponding parts of the graph of in the -axis.
Note that the sharp cusp on at unfolds into a smooth curve crossing the -axis in , which matches changing sign from positive to negative.
3. Determine the exact asymptotes and intercepts.
Applying the reflections in the -axis for and to the key features of the graph:
- The horizontal asymptote reflects to become .
- The -intercept reflects to become .
- The known -intercept remains .
- The smooth local minimum touching the -axis at the negative root remains an -intercept, becoming a local maximum.
- The vertical asymptotes and are unchanged.
Sketch of :
[A valid sketch should show the following features on a coordinate plane]
- : Curve approaching from above as , rising to touch the -axis at a negative -value (smooth local maximum), falling to cross the -axis at , and tending to as .
- : An inverted U-shaped curve entirely below the -axis, tending to as and as .
- : Curve starting from near , falling to cross the -axis smoothly at , and continuing to decrease while approaching from above as .
Equations of Asymptotes:
, ,
Coordinates of Points of Intersection:
-axis:
-axis: and an unknown negative coordinate .
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