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June 2013 p32 q3
1582
The variables x and y satisfy the equation y = Ae-kx2, where A and k are constants. The graph of ln y against x2 is a straight line passing through the points (0.64, 0.76) and (1.69, 0.32), as shown in the diagram. Find the values of A and k correct to 2 decimal places.
Solution
\(Given the equation y = Ae-kx2, taking the natural logarithm of both sides gives:\)
\(\ln y = \ln A - kx^2\)
This is in the form of a straight line \(y = mx + c\) with \(\ln y\) as the dependent variable and \(x^2\) as the independent variable. The slope \(m = -k\) and the intercept \(c = \ln A\).
Using the points (0.64, 0.76) and (1.69, 0.32), calculate the slope: