已知 和 都是正数常数,在同一幅图上,草拟以下函数的图像:
由此或通过其他方法,解不等式 。
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完整解法
7(a)
1. Determine the shape and key features of $y = \frac{2}{|x - a|}$.
The expression is always positive for , so is strictly positive.
As , the denominator approaches , so , meaning is a vertical asymptote.
As , , meaning the -axis () is a horizontal asymptote.
At , the -intercept is (since ).
2. Determine the shape and key features of $y = b|x - a|$.
The function is a modulus graph, which forms a 'V' shape opening upwards (since ).
The minimum point (vertex) occurs when , giving the coordinate .
At , the -intercept is .
3. Sketch both graphs on the same coordinate axes.
Draw the and axes.
Mark on the positive -axis and draw a vertical dotted line to represent the asymptote and axis of symmetry.
Plot the vertex and draw the straight V-shape lines for , labelling the -intercept .
Draw the two symmetric branches of approaching upwards and the -axis outwards, labelling the -intercept .
Ensure the graphs intersect exactly twice, once on each side of .
A single sketch containing:
- A vertical asymptote labelled .
- The V-shaped graph with vertex at and -intercept .
- The two-branch curve in the upper quadrants, approaching and , with -intercept .
- Both graphs intersecting at two points, one on each side of .
7(b)
1. Multiply both sides of the inequality by $|x - a|$ to eliminate the denominator, noting the condition for validity.
For the expression to be defined, .
For , we know that .
Since is strictly positive, we can multiply both sides of the inequality by without reversing the inequality sign:
2. Solve the resulting inequality for $x - a$.
Since is a positive constant (), we divide by :
Since and the square root of both sides gives :
Using the property of modulus inequalities ():
3. State the final solution set, excluding the value where the original expression is undefined.
The original inequality is undefined at .
Therefore, we must explicitly exclude from the solution interval.
or
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