图中给出了 y=f(∣x∣)y = \mathrm{f}(|x|) 和 y=f′(x)y = \mathrm{f}'(x) 的图像。 y=f(∣x∣)y = \mathrm{f}(|x|) 的图像在 (−3,4)(-3, 4) 和 (3,4)(3, 4) 处有转折点,交 xx 轴于 (−2,0)(-2, 0) 和 (2,0)(2, 0),其渐近线方程为 x=−1x = -1,x=1x = 1 和 y=2y = 2。y=f′(x)y = \mathrm{f}'(x) 的图像交 xx 轴于 (3,0)(3, 0),其渐近线方程为 x=1x = 1 和 y=0y = 0。 在不同的图中,分别草拟以下函数的图像,清晰标明任何渐近线方程、任何坐标轴交点以及转折点(若有)的坐标。

  1. (a)

    y=f(x)y = \mathrm{f}(x),

  2. (b)

    y=1f′(x)y = \frac{1}{\mathrm{f}'(x)},

  3. (c)

    y=−f(∣x−1∣)y = -\mathrm{f}(|x-1|),

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完整解法

1(a)

1. Determine the shape of the graph for $x \ge 0$ using the graph of $y = \mathrm{f}(|x|)$.

Since ∣x∣=x|x| = x for x≥0x \ge 0, the graph of y=f(x)y = \mathrm{f}(x) for x≥0x \ge 0 is exactly the right half of the given graph of y=f(∣x∣)y = \mathrm{f}(|x|).
From the given y=f(∣x∣)y = \mathrm{f}(|x|) graph, we extract the following features for x≥0x \ge 0:

  • The curve passes through the origin (0,0)(0,0).
  • There is a vertical asymptote at x=1x = 1, with the curve falling to −∞-\infty as x→1−x \to 1^-.
  • For x>1x > 1, the curve rises from −∞-\infty, crossing the xx-axis at (2,0)(2,0).
  • There is a local maximum turning point at (3,4)(3,4).
  • The curve approaches the horizontal asymptote y=2y = 2 from above as x→∞x \to \infty.

2. Determine the shape of the graph for $x < 0$ using the graph of $y = \mathrm{f}'(x)$.

For x<0x < 0, we refer to the given derivative graph y=f′(x)y = \mathrm{f}'(x).
The graph of y=f′(x)y = \mathrm{f}'(x) is entirely below the xx-axis for x<1x < 1, which means f′(x)<0\mathrm{f}'(x) < 0. Thus, y=f(x)y = \mathrm{f}(x) must be strictly decreasing for all x<1x < 1.
Furthermore, f′(x)→0\mathrm{f}'(x) \to 0 as x→−∞x \to -\infty, indicating that y=f(x)y = \mathrm{f}(x) approaches a horizontal asymptote. Matching the horizontal asymptote y=2y = 2 on the right side, f(x)→2\mathrm{f}(x) \to 2 as x→−∞x \to -\infty.
Therefore, for x<0x < 0, the curve of y=f(x)y = \mathrm{f}(x) is a smooth, monotonically decreasing curve that approaches y=2y = 2 from below as x→−∞x \to -\infty and passes through (0,0)(0,0). The asymptote x=−1x = -1 seen in the f(∣x∣)\mathrm{f}(|x|) graph is omitted as it was purely a reflection of x=1x = 1 due to the absolute value function.

答案

A sketch of y=f(x)y = \mathrm{f}(x) on Cartesian axes with the following features:

  • Asymptotes: Vertical dashed line at x=1x = 1 and horizontal dashed line at y=2y = 2.
  • Axial Intercepts: Passes through the origin (0,0)(0,0) and the xx-axis at (2,0)(2,0).
  • Turning Point: A local maximum at (3,4)(3,4).
  • Shape: For x<1x < 1, the curve approaches y=2y=2 from below as x→−∞x \to -\infty, decreases smoothly through (0,0)(0,0), and drops towards y→−∞y \to -\infty as it approaches x=1x=1 from the left. For x>1x > 1, it emerges from x=1x=1 at y→−∞y \to -\infty, rises to cross (2,0)(2,0), peaks at (3,4)(3,4), and decreases to approach y=2y=2 from above as x→∞x \to \infty.

1(b)

1. Determine the vertical asymptote(s) and axial intercept(s) of the reciprocal graph.

  • Vertical Asymptotes: These occur where the original function f′(x)=0\mathrm{f}'(x) = 0. From the given graph, f′(x)\mathrm{f}'(x) crosses the xx-axis at (3,0)(3, 0). Thus, x=3x = 3 is a vertical asymptote.
  • xx-intercepts: These occur where f′(x)→±∞\mathrm{f}'(x) \to \pm\infty. The given graph has a vertical asymptote at x=1x = 1. Thus, 1f′(x)=0\frac{1}{\mathrm{f}'(x)} = 0 at x=1x = 1, giving an xx-intercept at (1,0)(1, 0).
  • yy-intercept: Occurs at x=0x=0. Since f′(0)\mathrm{f}'(0) is a finite negative value, the yy-intercept is negative (exact value unknown).

2. Determine the behavior and shape of the graph for $x < 3$.

  • For x<1x < 1: f′(x)<0\mathrm{f}'(x) < 0. As x→−∞x \to -\infty, f′(x)→0−\mathrm{f}'(x) \to 0^-, meaning y→−∞y \to -\infty. The curve rises from the bottom left, crosses the negative yy-axis, and smoothly passes through (1,0)(1, 0).
  • For 1<x<31 < x < 3: f′(x)>0\mathrm{f}'(x) > 0. As x→3−x \to 3^-, f′(x)→0+\mathrm{f}'(x) \to 0^+, meaning y→∞y \to \infty. The curve continues upward from (1,0)(1, 0) to the vertical asymptote x=3x = 3.

3. Determine the behavior, shape, and turning points for $x > 3$.

  • For x>3x > 3: f′(x)<0\mathrm{f}'(x) < 0. As x→3+x \to 3^+, f′(x)→0−\mathrm{f}'(x) \to 0^-, so y→−∞y \to -\infty. As x→∞x \to \infty, f′(x)→0−\mathrm{f}'(x) \to 0^-, meaning y→−∞y \to -\infty.
  • The graph of f′(x)\mathrm{f}'(x) has a local minimum in the fourth quadrant. Correspondingly, its reciprocal y=1f′(x)y = \frac{1}{\mathrm{f}'(x)} will have a local maximum. Since the values are strictly negative in this region, the turning point (local maximum) lies below the xx-axis. Coordinates are marked as a turning point but remain unlabeled as exact values are not provided.
答案

A sketch of the graph y=1f′(x)y = \frac{1}{\mathrm{f}'(x)} showing:

  • Vertical Asymptote: x=3x = 3.
  • Axial Intercept: (1,0)(1, 0).
  • Shape for x<1x < 1: Curve comes from y→−∞y \to -\infty as x→−∞x \to -\infty, rises to cross the negative yy-axis, and passes through (1,0)(1, 0).
  • Shape for 1<x<31 < x < 3: Curve continues to rise from (1,0)(1, 0) towards y→∞y \to \infty as it approaches x=3x = 3 from the left.
  • Shape for x>3x > 3: Curve comes from y→−∞y \to -\infty as x→3+x \to 3^+, rises to a local maximum point below the xx-axis (coordinates unlabeled as they are not determinable), and then falls back to y→−∞y \to -\infty as x→∞x \to \infty.

1(c)

1. Identify the geometrical transformations connecting $y = \mathrm{f}(|x|)$ to $y = -\mathrm{f}(|x-1|)$.

Let g(x)=f(∣x∣)g(x) = \mathrm{f}(|x|). The target function is y=−f(∣x−1∣)=−g(x−1)y = -\mathrm{f}(|x-1|) = -g(x-1).
This represents two transformations applied to the given graph of y=f(∣x∣)y = \mathrm{f}(|x|):

  1. A translation of 11 unit in the positive xx-direction (x→x−1x \to x - 1).
  2. A reflection in the xx-axis (y→−yy \to -y).

2. Apply transformations to the asymptotes and intercepts.

Asymptotes:

  • The original vertical asymptotes are at x=−1x = -1 and x=1x = 1.
    Translating them by +1+1 gives x=0x = 0 and x=2x = 2. Reflection in the xx-axis does not affect vertical lines.
  • The original horizontal asymptote is at y=2y = 2.
    Translation does not affect it. Reflection in the xx-axis moves it to y=−2y = -2.

Axial Intercepts:

  • The original xx-intercepts are at (−2,0)(-2, 0), (0,0)(0, 0), and (2,0)(2, 0).
    Translating by +1+1 gives xx-intercepts at (−1,0)(-1, 0), (1,0)(1, 0), and (3,0)(3, 0). Reflection in the xx-axis leaves points on the xx-axis unchanged.
  • There is no yy-intercept because x=0x = 0 is a vertical asymptote.

3. Apply transformations to the turning points and describe the final shape.

Turning Points:

  • The original local maximums are at (−3,4)(-3, 4), (0,0)(0, 0), and (3,4)(3, 4).
  • Applying the translation (+1+1 to xx-coordinates) gives (−2,4)(-2, 4), (1,0)(1, 0), and (4,4)(4, 4).
  • Applying the reflection (negating yy-coordinates) turns them into local minimums at (−2,−4)(-2, -4), (1,0)(1, 0), and (4,−4)(4, -4).

The final graph consists of three branches separated by the vertical asymptotes, opening upwards towards +∞+\infty near the asymptotes, and approaching y=−2y = -2 from below as x→±∞x \to \pm\infty.

答案

A sketch with the following key features:

  • Vertical asymptotes: x=0x = 0 (the yy-axis) and x=2x = 2
  • Horizontal asymptote: y=−2y = -2
  • xx-intercepts: (−1,0)(-1, 0), (1,0)(1, 0), and (3,0)(3, 0)
  • Turning points (all local minimums): (−2,−4)(-2, -4), (1,0)(1, 0), and (4,−4)(4, -4)
  • The curve approaches y=−2y = -2 from below as x→±∞x \to \pm\infty and approaches +∞+\infty near the vertical asymptotes.

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