用 aa 表示方程 1(x−a)2=∣x−a∣\dfrac{1}{(x-a)^2}=|x-a| 的根。 在同一坐标系中,画出方程为 y=1(x−a)2y=\dfrac{1}{(x-a)^2} 和 y=∣x−a∣y=|x-a| 的曲线草图,其中 a>1a>1。 由此解不等式 1(x−a)2>∣x−a∣\dfrac{1}{(x-a)^2}>|x-a|。

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完整解法

2(i)

1. Rewrite the equation using the property that $(x-a)^2 = |x-a|^2$.

Since (x−a)2=∣x−a∣2(x-a)^2 = |x-a|^2, the equation can be rewritten as:
1∣x−a∣2=∣x−a∣\frac{1}{|x-a|^2} = |x-a|

2. Rearrange and solve for $|x-a|$.

1=∣x−a∣31 = |x-a|^3
∣x−a∣=1|x-a| = 1

3. Solve the linear modulus equation for $x$.

x−a=1orx−a=−1x - a = 1 \quad \text{or} \quad x - a = -1
x=a+1orx=a−1x = a + 1 \quad \text{or} \quad x = a - 1

答案

x=a+1x = a+1 or x=a−1x = a-1

2(ii)

1. Calculate the roots of the equation from part (i) to find the intersection points of the two graphs.

From part (i), we solve 1(x−a)2=∣x−a∣\dfrac{1}{(x-a)^2} = |x-a|:
Multiplying both sides by ∣x−a∣2|x-a|^2 (assuming x≠ax \neq a) gives:
1=∣x−a∣3  ⟹  ∣x−a∣=11 = |x-a|^3 \implies |x-a| = 1
x−a=1orx−a=−1x - a = 1 \quad \text{or} \quad x - a = -1
x=a+1orx=a−1x = a+1 \quad \text{or} \quad x = a-1
The yy-coordinate for both points is y=∣(a±1)−a∣=1y = |(a \pm 1) - a| = 1.
Thus, the intersection points are (a−1,1)(a-1, 1) and (a+1,1)(a+1, 1).

2. Identify the key features of both graphs to sketch them on the same axes.

Curve y=1(x−a)2y=\dfrac{1}{(x-a)^2}:

  • Vertical asymptote at x=ax=a and horizontal asymptote at y=0y=0.
  • yy-intercept at (0,1a2)(0, \dfrac{1}{a^2}).
  • The curve lies entirely above the xx-axis, approaching infinity as x→ax \to a.

Graph y=∣x−a∣y=|x-a|:

  • V-shape with its minimum point (vertex) at (a,0)(a, 0).
  • yy-intercept at (0,a)(0, a).

Sketch details:
Since a>1a > 1, we have a>1a2a > \dfrac{1}{a^2}, so the V-shape intersects the yy-axis higher than the curve. Because a>1  ⟹  a−1>0a > 1 \implies a-1 > 0, both intersection points (a−1,1)(a-1, 1) and (a+1,1)(a+1, 1) lie in the positive xx-axis region. Draw these features clearly on the axes.

3. Use the sketched graphs to solve the given inequality.

The inequality 1(x−a)2>∣x−a∣\dfrac{1}{(x-a)^2} > |x-a| requires the curve y=1(x−a)2y=\dfrac{1}{(x-a)^2} to be strictly above the V-shaped graph y=∣x−a∣y=|x-a|.
From the sketch, the curve is above the V-shape between the two intersection points x=a−1x=a-1 and x=a+1x=a+1.
However, the curve is undefined at the vertical asymptote x=ax=a, so this value must be excluded from the region.
Therefore, the solution is:
a−1<x<aora<x<a+1a-1 < x < a \quad \text{or} \quad a < x < a+1

答案

a−1<x<aora<x<a+1a-1 < x < a \quad \text{or} \quad a < x < a+1

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