下图显示了 y = f(x) 的图像。曲线在 (-2, 0) 和 (1, 0) 处穿过 x 轴,并且具有坐标为 (2, 2) 的极大值点。直线 x = -1 和 y = 1 是该图像的渐近线。 在可能的情况下,指出所有渐近线的方程、与坐标轴的交点坐标以及驻点坐标,画出以下函数的图像:
- (a)
y = 3 f(x + a),其中 a 是一个正常数且满足 1 < a < 2 ,
- (b)
y = f'(x)。
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完整解法
2(a)
1. Identify the geometrical transformations represented by the equation.
The equation is . Compared to the original graph of , this represents:
- A horizontal translation by units in the negative -direction (to the left).
- A vertical stretch by a scale factor of 3 parallel to the -axis.
2. Determine the new equations of the asymptotes.
Applying the transformations to the original asymptotes:
- The vertical asymptote is translated units left, becoming .
- The horizontal asymptote is unaffected by the horizontal translation but is stretched vertically by a factor of 3, becoming .
3. Find the coordinates of the transformed $x$-intercepts and stationary point, and verify their graphical positions.
Applying the transformations to the known points:
- For the -intercepts and , the -coordinates remain . The -coordinates are translated to give new intercepts at and .
- For the maximum point , the -coordinate is shifted by and the -coordinate is multiplied by . The new maximum is at .
Given the condition :
- is between and , so the intercept must be drawn on the negative -axis.
- is between and , so the maximum point must be drawn in the first quadrant (to the right of the -axis).
- Since the maximum is to the right of the -axis and the -intercept is to the left, the curve's -intercept will be positive.
A sketch of the curve with the following features:
- Asymptotes: Vertical line and horizontal line .
- -intercepts: and . Note that since , the intercept is on the negative -axis.
- Maximum point: . Since , this point lies in the first quadrant.
- -intercept: The curve intersects the positive -axis.
- The shape is vertically stretched and shifted left, preserving the two-branch structure of the original curve.
2(b)
1. Determine the coordinates of the intersection with the $x$-axis.
The graph of has a maximum point at , which means the gradient at is zero.
Therefore, , giving an -intercept at for the graph of .
2. Determine the equations of the asymptotes.
As , the graph of approaches the horizontal asymptote , meaning the gradient approaches . Thus, (the -axis) is a horizontal asymptote for .
As , approaches the vertical asymptote . Because the curve falls to on both sides of , the gradient as and as . Thus, is a vertical asymptote for .
3. Determine the signs of $f'(x)$ and the presence of stationary points to deduce the final shape.
By observing the increasing/decreasing nature of :
- For , is decreasing (curve below -axis).
- For , is increasing (curve above -axis).
- For , is decreasing (curve below -axis).
Since and as , the continuous graph of must reach a local minimum at some point where before approaching the -axis from below. (Exact coordinates of this stationary point and the -intercept cannot be deduced).
Features to be shown on the sketch of :
- -intercept:
- Vertical asymptote:
- Horizontal asymptote:
- Turning point: A local minimum for some (exact coordinates cannot be determined).
- Shape and Signs:
- : Curve is entirely below the -axis, starting near as and going to as .
- : Curve is entirely above the -axis, coming from as and decreasing to intersect the -axis at .
- : Curve is below the -axis, decreasing to a minimum before increasing back towards as .
(A sketch incorporating these features would be drawn on the Cartesian plane.)
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