下表显示了两个变量 x 和 y 的实验值,它们由 y=kxny = \frac{k}{x^{n}} 形式的方程联系在一起,其中 n 和 k 是常数。

  1. (a)

    绘制 lg⁡y\lg y 关于 lg⁡x\lg x 的图表,并画出一条直线来展示这些信息。

  2. (b)

    利用你的图表估算 kk 和 nn 的值。

  3. (c)

    通过在同一坐标系上画出另一条直线,估算使得 lg⁡y=lg⁡x2\lg y = \lg x^{2} 的 xx 的值。

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完整解法

2(a)

1. Calculate the values of $\lg x$ and $\lg y$ for each data point, rounding to 2 decimal places.

For x=1.58x = 1.58, lg⁡x≈0.20\lg x \approx 0.20. For y=20.89y = 20.89, lg⁡y≈1.32\lg y \approx 1.32.
For x=2.00x = 2.00, lg⁡x≈0.30\lg x \approx 0.30. For y=15.14y = 15.14, lg⁡y≈1.18\lg y \approx 1.18.
For x=5.01x = 5.01, lg⁡x≈0.70\lg x \approx 0.70. For y=4.37y = 4.37, lg⁡y≈0.64\lg y \approx 0.64.
For x=13.80x = 13.80, lg⁡x≈1.14\lg x \approx 1.14. For y=1.10y = 1.10, lg⁡y≈0.04\lg y \approx 0.04.

lg⁡x\lg x0.200.300.701.14
lg⁡y\lg y1.321.180.640.04

2. Plot the points on a Cartesian plane and draw the line of best fit.

Choose appropriate scales for the axes (e.g., 2 cm2\text{ cm} to 0.20.2 units on both axes).
Plot the points (0.20,1.32)(0.20, 1.32), (0.30,1.18)(0.30, 1.18), (0.70,0.64)(0.70, 0.64), and (1.14,0.04)(1.14, 0.04).
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 (0.20,1.32)(0.20, 1.32), (0.30,1.18)(0.30, 1.18), (0.70,0.64)(0.70, 0.64), and (1.14,0.04)(1.14, 0.04).

2(b)

1. Transform the given non-linear equation into a linear form involving $\lg y$ and $\lg x$.

y=kxny = \frac{k}{x^n}
lg⁡y=lg⁡(kxn)\lg y = \lg \left(\frac{k}{x^n}\right)
lg⁡y=lg⁡k−lg⁡xn\lg y = \lg k - \lg x^n
lg⁡y=−nlg⁡x+lg⁡k\lg y = -n \lg x + \lg k

2. Calculate the gradient of the line to estimate $n$.

Using points from the table to find the gradient of the line of best fit (or using the theoretical points if the line passes through them perfectly):
Let's use (x1,y1)=(1.58,20.89)(x_1, y_1) = (1.58, 20.89) and (x2,y2)=(13.80,1.10)(x_2, y_2) = (13.80, 1.10).
lg⁡x1=lg⁡1.58≈0.1987\lg x_1 = \lg 1.58 \approx 0.1987
lg⁡y1=lg⁡20.89≈1.3199\lg y_1 = \lg 20.89 \approx 1.3199
lg⁡x2=lg⁡13.80≈1.1399\lg x_2 = \lg 13.80 \approx 1.1399
lg⁡y2=lg⁡1.10≈0.0414\lg y_2 = \lg 1.10 \approx 0.0414

Gradient=0.0414−1.31991.1399−0.1987=−1.27850.9412≈−1.358\text{Gradient} = \frac{0.0414 - 1.3199}{1.1399 - 0.1987} = \frac{-1.2785}{0.9412} \approx -1.358
Since gradient =−n= -n, n≈1.36n \approx 1.36 (accept 1.351.35 to 1.371.37).

3. Calculate the vertical intercept to estimate $k$.

Using the equation lg⁡y=−1.358lg⁡x+lg⁡k\lg y = -1.358 \lg x + \lg k and the point (0.1987,1.3199)(0.1987, 1.3199):
1.3199=−1.358(0.1987)+lg⁡k1.3199 = -1.358(0.1987) + \lg k
1.3199=−0.2698+lg⁡k1.3199 = -0.2698 + \lg k
lg⁡k=1.5897\lg k = 1.5897
k=101.5897≈38.9k = 10^{1.5897} \approx 38.9 (accept 38.038.0 to 40.040.0 depending on the line of best fit).

答案

n=1.35n = 1.35, k=38.0k = 38.0

2(c)

1. Identify the equation of the straight line to be drawn

The given equation is lg⁡y=lg⁡x2\lg y = \lg x^{2}.
Using the power law of logarithms, this simplifies to lg⁡y=2lg⁡x\lg y = 2\lg x.
Letting Y=lg⁡yY = \lg y and X=lg⁡xX = \lg x, the line to draw is Y=2XY = 2X.

2. Find the intersection point and solve for x

Draw the line Y=2XY = 2X on the same axes.
From the graph, the intersection of this line with the line of best fit occurs at approximately X=0.473X = 0.473.
Since X=lg⁡xX = \lg x, we have lg⁡x=0.473\lg x = 0.473.
x=100.473≈2.97x = 10^{0.473} \approx 2.97

答案

x≈2.97x \approx 2.97

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