The table below shows experimental values of two variables and . It is known that and are related by an equation of the form , where and are constants.
1 2 3 4 5 6 5.2 7.2 9.1 10.9 12.6 14.2
| 1 | 2 | 3 | 4 | 5 | 6 | |
|---|---|---|---|---|---|---|
| 5.2 | 7.2 | 9.1 | 10.9 | 12.6 | 14.2 |
- (i)
Draw the graph of plotted against , using a scale of 2 cm to 0.1 unit on both axes.
- (ii)
Use your graph to estimate the value of each of the constants and .
- (iii)
Explain how the value of when can be estimated using the straight line graph.
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Worked solution
3(i)
1. Calculate the values of $X = \lg(1+x)$ and $Y = \lg y$ for each data point.
For : ,
For : ,
For : ,
For : ,
For : ,
For : ,
2. Plot the points on the grid and draw the line of best fit.
Plot the points , , , , , on axes with scale 2 cm to 0.1 unit.
Draw a straight line of best fit passing through or close to these points.
A straight line graph plotted with points , , , , , .
3(ii)
1. Convert the non-linear equation to linear form using logarithms
2. Identify the gradient and $Y$-intercept from the linear form
Comparing with :
Gradient
-intercept
3. Calculate the gradient to find $k$
Using points from the line of best fit, e.g., and :
(Acceptable range for : to )
4. Find the $Y$-intercept to calculate $h$
From the graph, the -intercept is approximately .
(Acceptable range for : to )
,
3(iii)
1. Explain the process of finding the corresponding $y$ value from the graph
Calculate the value on the horizontal axis: .
Read the corresponding value on the vertical axis from the graph, which gives .
Calculate using .
Calculate . Find this value on the horizontal axis and read the corresponding value on the vertical axis to get . Finally, calculate .
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