图中显示了曲线 ,其极值点为 和 。直线 和 是该曲线的渐近线。

- (a)
在不同的图上分别画出下列函数的图像,并视情况清晰写出渐近线的方程以及对应于 A 和 B 的点的坐标。
- (i)
- (ii)
- (i)
- (b)
已知一曲线的参数方程为
。
该曲线关于 轴反射。求反射后的曲线与 轴交点的精确坐标。
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完整解法
4(a)(i)
1. Identify the geometrical transformations applied to the original graph.
The equation represents a translation of the graph of by units in the positive -direction (to the right) and units in the positive -direction (upwards).
2. Find the coordinates of the new turning points.
Point
Point
3. Find the equations of the new asymptotes.
Vertical asymptote: (the -axis)
Horizontal asymptote:
A sketch of the curve with the same shape as , but shifted. The new turning points are and . The new asymptotes are (the -axis) and .
4(a)(ii)
1. Determine the asymptotes of y = f'(x)
The vertical asymptote of is unchanged, so is still a vertical asymptote of ; near it increases steeply to , so as .
Since is a horizontal asymptote of , the curve flattens as , so . Hence the horizontal asymptote of is (the -axis).
2. Convert turning points of f into x-intercepts of f'
At a turning point the gradient is zero, so at the -coordinates of and .
- -intercept .
- -intercept .
3. Use sign of the gradient on each interval to sketch f'
Read off the gradient of on each interval (B is a minimum, A is a maximum):
- : decreasing (below axis, from up to at ).
- : increasing (above axis, a positive hump).
- : decreasing towards , approaching .
Sketch a curve rising from near , crossing the axis at , peaking, crossing back at , then staying just below the -axis and tending to .
Sketch of with:
- Vertical asymptote (curve as ).
- Horizontal asymptote (curve as ).
- -intercepts at (from ) and (from ).
- for , for , for .
4(b)
1. Set $y = 0$ to find the value of the parameter $t$ at the $x$-axis intercept.
Since the domain restricts , we have .
2. Find the original $x$-coordinate, apply the reflection in the $y$-axis, and state the final exact coordinates.
Original -coordinate at :
When a curve is reflected in the -axis, its -coordinates remain unchanged and its -coordinates are negated.
Reflected -coordinate:
The exact coordinates of the point are .
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