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June 2020 p32 q2
1578
The variables x and y satisfy the equation y2 = Aekx, where A and k are constants. The graph of ln y against x is a straight line passing through the points (1.5, 1.2) and (5.24, 2.7) as shown in the diagram.
Find the values of A and k correct to 2 decimal places.
Solution
\(Given the equation y2 = Aekx, take the natural logarithm of both sides:\)
\(2 ln y = ln A + kx.\)
This is in the form of a straight line equation y = mx + c, where the slope m is k and the intercept c is ln A.
Using the points (1.5, 1.2) and (5.24, 2.7), calculate the slope k:
k = \(\frac{2.7 - 1.2}{5.24 - 1.5} \approx 0.80\).
Substitute k = 0.80 into the equation 2 ln y = ln A + 0.80x and use one of the points to find ln A: