The table shows experimental values of two variables, x and y, which are connected by an equation of the form , where n and k are constants.

- (a)
Plot against and draw a straight line graph to illustrate this information.

- (b)
Use your graph to estimate the value of and .
- (c)
By drawing another straight line on the same axes, estimate the value of for which .
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Worked solution
2(a)
1. Calculate the values of $\lg x$ and $\lg y$ for each data point, rounding to 2 decimal places.
For , . For , .
For , . For , .
For , . For , .
For , . For , .
| 0.20 | 0.30 | 0.70 | 1.14 | |
|---|---|---|---|---|
| 1.32 | 1.18 | 0.64 | 0.04 |
2. Plot the points on a Cartesian plane and draw the line of best fit.
Choose appropriate scales for the axes (e.g., to units on both axes).
Plot the points , , , and .
Draw a straight line passing through or as close as possible to all the plotted points.
A straight line graph plotted with points , , , and .
2(b)
1. Transform the given non-linear equation into a linear form involving $\lg y$ and $\lg x$.
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 and .
Since gradient , (accept to ).
3. Calculate the vertical intercept to estimate $k$.
Using the equation and the point :
(accept to depending on the line of best fit).
,
2(c)
1. Identify the equation of the straight line to be drawn
The given equation is .
Using the power law of logarithms, this simplifies to .
Letting and , the line to draw is .
2. Find the intersection point and solve for x
Draw the line on the same axes.
From the graph, the intersection of this line with the line of best fit occurs at approximately .
Since , we have .
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