下表给出了两个变量 xx 和 yy 的实验值,它们通过方程 y=aebx−1y = ae^{bx - 1} 相关联,其中 aa 和 bb 为常数。
xx12345
yy1.892.32.823.444.20

  1. (a)

    在第 23 页给出的网格中,使用横轴上 2 cm 表示 1 个单位,纵轴上 2 cm 表示 0.2 个单位的比例,绘制 ln⁡y\ln y 关于 xx 的直线图。

    [提供用于绘制 ln⁡y\ln y 关于 xx 的直线图的坐标纸。]

  2. (b)

    利用你的图表估算 aa 和 bb 的值。

  3. (c)

    通过在图上画出一条合适的直线,解方程 2.46=aebx−12.46 = ae^{bx - 1}。

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完整解法

12(a)

1. Calculate the values of $\ln y$ for each corresponding $x$ value.

Using the given yy values, we compute ln⁡y\ln y to 2 decimal places:

  • x=1x = 1: ln⁡(1.89)≈0.64\ln(1.89) \approx 0.64
  • x=2x = 2: ln⁡(2.3)≈0.83\ln(2.3) \approx 0.83
  • x=3x = 3: ln⁡(2.82)≈1.04\ln(2.82) \approx 1.04
  • x=4x = 4: ln⁡(3.44)≈1.24\ln(3.44) \approx 1.24
  • x=5x = 5: ln⁡(4.20)≈1.44\ln(4.20) \approx 1.44

2. Set up the axes and plot the points.

Draw the horizontal axis for xx with a scale of 2 cm to 1 unit (from x=0x=0 to x=5x=5).
Draw the vertical axis for ln⁡y\ln y with a scale of 2 cm to 0.2 units (from ln⁡y=0.6\ln y = 0.6 to ln⁡y=1.6\ln y = 1.6).
Plot the points (1,0.64)(1, 0.64), (2,0.83)(2, 0.83), (3,1.04)(3, 1.04), (4,1.24)(4, 1.24), and (5,1.44)(5, 1.44).

3. Draw the line of best fit.

Draw a straight line passing through or as close as possible to all the plotted points.

答案

A straight line graph plotted with points (1,0.64)(1, 0.64), (2,0.83)(2, 0.83), (3,1.04)(3, 1.04), (4,1.24)(4, 1.24), and (5,1.44)(5, 1.44).

12(b)

1. Transform the non-linear equation into linear form

y=aebx−1y = ae^{bx - 1}
ln⁡y=ln⁡(aebx−1)\ln y = \ln(ae^{bx - 1})
ln⁡y=ln⁡a+ln⁡(ebx−1)\ln y = \ln a + \ln(e^{bx - 1})
ln⁡y=ln⁡a+(bx−1)\ln y = \ln a + (bx - 1)
ln⁡y=bx+(ln⁡a−1)\ln y = bx + (\ln a - 1)

2. Calculate the gradient to find $b$

From the table, the points (x,ln⁡y)(x, \ln y) are approximately:
(1,0.637),(2,0.833),(3,1.037),(4,1.235),(5,1.435)(1, 0.637), (2, 0.833), (3, 1.037), (4, 1.235), (5, 1.435)
Gradient m=b=1.435−0.6375−1=0.7984=0.1995≈0.20m = b = \frac{1.435 - 0.637}{5 - 1} = \frac{0.798}{4} = 0.1995 \approx 0.20

3. Calculate the vertical intercept to find $a$

Vertical intercept c=ln⁡a−1c = \ln a - 1
Using point (1,0.637)(1, 0.637) and m=0.20m = 0.20:
0.637=0.20(1)+c  ⟹  c=0.4370.637 = 0.20(1) + c \implies c = 0.437
ln⁡a−1=0.437\ln a - 1 = 0.437
ln⁡a=1.437\ln a = 1.437
a=e1.437≈4.21a = e^{1.437} \approx 4.21
(Note: Reading the intercept directly from the graph at x=0x=0 gives c≈0.44c \approx 0.44, so ln⁡a−1=0.44  ⟹  ln⁡a=1.44  ⟹  a=e1.44≈4.22\ln a - 1 = 0.44 \implies \ln a = 1.44 \implies a = e^{1.44} \approx 4.22. Acceptable range for aa is typically 4.14.1 to 4.34.3, and bb is 0.190.19 to 0.210.21.)

答案

a=1.40a = 1.40, b=0.20b = 0.20

12(c)

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

The original equation is y=aebx−1y = ae^{bx - 1}.
We are asked to solve 2.46=aebx−12.46 = ae^{bx - 1}, which corresponds to y=2.46y = 2.46.
Since the vertical axis of the graph is ln⁡y\ln y, we take the natural logarithm:
ln⁡y=ln⁡2.46\ln y = \ln 2.46
ln⁡y≈0.900\ln y \approx 0.900

2. Determine the solution from the graph

Draw the horizontal line ln⁡y=0.90\ln y = 0.90 on the graph.
Find the xx-coordinate of the point of intersection between this horizontal line and the plotted straight line.
Reading from the graph, x≈2.32x \approx 2.32.

答案

x≈2.32x \approx 2.32

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