1. (i)

    画出方程为 y=x−2x−1y = \frac{x-2}{x-1} 的曲线 CC 的草图,写出其与坐标轴的交点的精确坐标以及所有渐近线的方程。

  2. (ii)

    通过在草图中添加一条直线,解不等式 x−2x−1≤2−x\frac{x-2}{x-1} \le 2-x。

  3. (iii)

    由此,解不等式 ∣x∣−2∣x∣−1≤2−∣x∣\frac{|x|-2}{|x|-1} \le 2-|x|。

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完整解法

2(i)

1. Find the equations of the vertical and horizontal asymptotes.

The vertical asymptote occurs where the denominator is zero:
x−1=0  ⟹  x=1x - 1 = 0 \implies x = 1

The horizontal asymptote is found by examining the behaviour as x→±∞x \to \pm\infty, or by polynomial division:
y=x−2x−1=x−1−1x−1=1−1x−1y = \frac{x-2}{x-1} = \frac{x-1-1}{x-1} = 1 - \frac{1}{x-1}
As x→±∞x \to \pm\infty, 1x−1→0\frac{1}{x-1} \to 0, so the horizontal asymptote is:
y=1y = 1

2. Determine the exact coordinates of the intersections with the axes.

For the xx-axis intersection, substitute y=0y = 0:
0=x−2x−1  ⟹  x−2=0  ⟹  x=20 = \frac{x-2}{x-1} \implies x - 2 = 0 \implies x = 2
Coordinates are (2,0)(2, 0).

For the yy-axis intersection, substitute x=0x = 0:
y=0−20−1=2y = \frac{0-2}{0-1} = 2
Coordinates are (0,2)(0, 2).

3. Sketch the curve, clearly labelling the asymptotes and intercepts.

[Sketch of a hyperbola with dashed lines for asymptotes x=1x = 1 and y=1y = 1.
The top-left branch passes through the yy-intercept (0,2)(0, 2) and approaches both asymptotes.
The bottom-right branch passes through the xx-intercept (2,0)(2, 0) and approaches both asymptotes.]

答案

Asymptotes: x=1,y=1x = 1, y = 1
Intercepts: (2,0),(0,2)(2, 0), (0, 2)
[A smooth hyperbolic curve with branches in the top-left and bottom-right relative to the asymptotes' intersection at (1,1)(1,1)]

2(ii)

1. Identify the equation of the line to be drawn.

To solve x−2x−1≤2−x\frac{x-2}{x-1} \le 2-x graphically, we use the sketched curve CC with equation y=x−2x−1y = \frac{x-2}{x-1}.
We must draw the additional line y=2−xy = 2-x on the same axes.

2. Determine the points of intersection between the curve and the line.

The line y=2−xy = 2-x has an xx-intercept at (2,0)(2, 0) and a yy-intercept at (0,2)(0, 2).
These coordinates exactly match the axes intercepts of the curve CC found in part (i), meaning the line intersects the curve exactly at the points (0,2)(0, 2) and (2,0)(2, 0).

3. Use the graph to deduce the solution to the inequality.

The inequality x−2x−1≤2−x\frac{x-2}{x-1} \le 2-x is satisfied where the curve CC lies below or on the line y=2−xy = 2-x.
Observing the relative positions of the graphs and noting the vertical asymptote at x=1x = 1:

  • For x≤0x \le 0, the curve is below or on the line.
  • For 0<x<10 < x < 1, the curve is above the line.
  • For 1<x≤21 < x \le 2, the curve is below or on the line (excluding the asymptote x=1x = 1).
  • For x>2x > 2, the curve is above the line.

Thus, the required range of values is x≤0 or 1<x≤2x \le 0 \text{ or } 1 < x \le 2.

答案

x≤0 or 1<x≤2x \le 0 \text{ or } 1 < x \le 2

2(iii)

1. Concisely find the solution to the inequality from part (ii).

From part (ii), we solve x−2x−1≤2−x\frac{x-2}{x-1} \le 2-x:
x−2x−1−(2−x)≤0\frac{x-2}{x-1} - (2-x) \le 0
x−2−(2−x)(x−1)x−1≤0\frac{x-2 - (2-x)(x-1)}{x-1} \le 0
x(x−2)x−1≤0\frac{x(x-2)}{x-1} \le 0
The critical values are x=0x=0, x=1x=1 (asymptote), and x=2x=2. Evaluating the signs in the intervals between these values yields the solution for part (ii):
x≤0or1<x≤2x \le 0 \quad \text{or} \quad 1 < x \le 2

2. Apply the substitution $x \to |x|$ into the solution from part (ii).

The inequality in (iii) is identical to (ii) except xx is replaced by ∣x∣|x|. Thus, we substitute ∣x∣|x| into our solution:
∣x∣≤0or1<∣x∣≤2|x| \le 0 \quad \text{or} \quad 1 < |x| \le 2

3. Solve the resulting modulus inequalities.

For the first condition, since ∣x∣≥0|x| \ge 0 for all real xx:
∣x∣≤0  ⟹  ∣x∣=0  ⟹  x=0|x| \le 0 \implies |x| = 0 \implies x = 0

For the second condition, solving the compound modulus inequality 1<∣x∣≤21 < |x| \le 2 yields:
−2≤x<−1or1<x≤2-2 \le x < -1 \quad \text{or} \quad 1 < x \le 2

Combining these conditions gives the final solution set:
−2≤x<−1orx=0or1<x≤2-2 \le x < -1 \quad \text{or} \quad x = 0 \quad \text{or} \quad 1 < x \le 2

答案

−2≤x<−1 or x=0 or 1<x≤2-2 \le x < -1 \text{ or } x = 0 \text{ or } 1 < x \le 2

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