下表给出了两个变量 xx 与 yy 的实验值。已知 xx 与 yy 通过形如 y=h(x+1)ky = h(x+1)^k 的方程相关联,其中 hh 和 kk 为常数。
xx123456
yy5.27.29.110.912.614.2

  1. (i)

    以两轴均 2 cm 代表 0.1 个单位的比例,绘制 lg⁡y\lg y 关于 lg⁡(1+x)\lg(1+x) 的图象。

  2. (ii)

    利用你的图象估计常数 hh 和 kk 的值。

  3. (iii)

    解释如何利用该直线图象估计当 x=1.5x = 1.5 时 yy 的值。

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完整解法

3(i)

1. Calculate the values of $X = \lg(1+x)$ and $Y = \lg y$ for each data point.

For x=1,y=5.2x=1, y=5.2: X=lg⁡(2)≈0.301X = \lg(2) \approx 0.301, Y=lg⁡(5.2)≈0.716Y = \lg(5.2) \approx 0.716
For x=2,y=7.2x=2, y=7.2: X=lg⁡(3)≈0.477X = \lg(3) \approx 0.477, Y=lg⁡(7.2)≈0.857Y = \lg(7.2) \approx 0.857
For x=3,y=9.1x=3, y=9.1: X=lg⁡(4)≈0.602X = \lg(4) \approx 0.602, Y=lg⁡(9.1)≈0.959Y = \lg(9.1) \approx 0.959
For x=4,y=10.9x=4, y=10.9: X=lg⁡(5)≈0.699X = \lg(5) \approx 0.699, Y=lg⁡(10.9)≈1.037Y = \lg(10.9) \approx 1.037
For x=5,y=12.6x=5, y=12.6: X=lg⁡(6)≈0.778X = \lg(6) \approx 0.778, Y=lg⁡(12.6)≈1.100Y = \lg(12.6) \approx 1.100
For x=6,y=14.2x=6, y=14.2: X=lg⁡(7)≈0.845X = \lg(7) \approx 0.845, Y=lg⁡(14.2)≈1.152Y = \lg(14.2) \approx 1.152

2. Plot the points on the grid and draw the line of best fit.

Plot the points (0.301,0.716)(0.301, 0.716), (0.477,0.857)(0.477, 0.857), (0.602,0.959)(0.602, 0.959), (0.699,1.037)(0.699, 1.037), (0.778,1.100)(0.778, 1.100), (0.845,1.152)(0.845, 1.152) on axes with scale 2 cm to 0.1 unit.
Draw a straight line of best fit passing through or close to these points.

答案

A straight line graph plotted with points (0.301,0.716)(0.301, 0.716), (0.477,0.857)(0.477, 0.857), (0.602,0.959)(0.602, 0.959), (0.699,1.037)(0.699, 1.037), (0.778,1.100)(0.778, 1.100), (0.845,1.152)(0.845, 1.152).

3(ii)

1. Convert the non-linear equation to linear form using logarithms

y=h(x+1)ky = h(x+1)^k
lg⁡y=lg⁡(h(x+1)k)\lg y = \lg(h(x+1)^k)
lg⁡y=lg⁡h+klg⁡(x+1)\lg y = \lg h + k \lg(x+1)

2. Identify the gradient and $Y$-intercept from the linear form

Comparing lg⁡y=klg⁡(x+1)+lg⁡h\lg y = k \lg(x+1) + \lg h with Y=mX+cY = mX + c:
Gradient m=km = k
YY-intercept c=lg⁡hc = \lg h

3. Calculate the gradient to find $k$

Using points from the line of best fit, e.g., (0.30,0.72)(0.30, 0.72) and (0.85,1.00)(0.85, 1.00):
k=1.00−0.720.85−0.30=0.280.55≈0.51k = \frac{1.00 - 0.72}{0.85 - 0.30} = \frac{0.28}{0.55} \approx 0.51
(Acceptable range for kk: 0.500.50 to 0.540.54)

4. Find the $Y$-intercept to calculate $h$

From the graph, the YY-intercept is approximately 0.560.56.
lg⁡h=0.56\lg h = 0.56
h=100.56≈3.63h = 10^{0.56} \approx 3.63
(Acceptable range for hh: 3.53.5 to 3.83.8)

答案

h≈3.63h \approx 3.63, k≈0.52k \approx 0.52

3(iii)

1. Explain the process of finding the corresponding $y$ value from the graph

Calculate the value on the horizontal axis: lg⁡(1+1.5)=lg⁡2.5\lg(1+1.5) = \lg 2.5.
Read the corresponding value on the vertical axis from the graph, which gives lg⁡y\lg y.
Calculate yy using y=10lg⁡yy = 10^{\lg y}.

答案

Calculate lg⁡(1+1.5)=lg⁡2.5\lg(1+1.5) = \lg 2.5. Find this value on the horizontal axis and read the corresponding value on the vertical axis to get lg⁡y\lg y. Finally, calculate y=10lg⁡yy = 10^{\lg y}.

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