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Problem 105

How would you check whether data points of the form $\left(1, y_{1}\right),\left(2, y_{2}\right),\left(3, y_{3}\right)$ lie on an exponential curve?

Short Answer

Expert verified
To check if the data points \((1, y_1), (2, y_2), (3, y_3)\) lie on an exponential curve, plug the points into the exponential function \(y=ab^x\) and solve for constants \(a\) and \(b\). We get the equations \(y_1=ab\), \(y_2 = ab^2\), and \(y_3 = ab^3\). Solve for \(b\) by setting the ratio of the second and first equations equal to the ratio of the third and second equations, giving us \(\frac{y_2}{y_1}=\frac{y_3}{y_2}\). Then, solve for \(y_2^2 =y_1y_3\), and obtain unique values for \(a = \frac{y_1^2}{y_2}\) and \(b= \frac{y_2}{y_1}\). Since we have unique values for \(a\) and \(b\), the data points lie on an exponential curve of the form \(y = ab^x\).
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Step 1: Setup the exponential function with the data points

We have the data points \((1, y_1), (2, y_2), (3, y_3)\) and the exponential function \(y=ab^x\). Let's plug the given points into the function: For point (1, \(y_1\)): \(y_1=ab^1\) For point (2, \(y_2\)): \(y_2=ab^2\) For point (3, \(y_3\)): \(y_3=ab^3\)

Step 2: Solve for the constants a and b

Divide the second equation by the first equation, and the third equation by the second equation: \(\frac{y_2}{y_1} =\frac{ab^2}{ab^1} \Rightarrow \frac{y_2}{y_1}=b\) \(\frac{y_3}{y_2}=\frac{ab^3}{ab^2} \Rightarrow \frac{y_3}{y_2}=b\) Now since both fractions equal b, we can set them equal to each other: \(\frac{y_2}{y_1}=\frac{y_3}{y_2}\) Solve for \(y_2\): \(y_2^2 =y_1y_3\)

Step 3: Verify Constants a and b

Now that we have an equation for \(y_2\), we can plug back into the first equation and solve for \(a\): \(y_1=ab\) \(a= \frac{y_1}{b}=\frac{y_1}{\frac{y_2}{y_1}} = \frac{y_1^2}{y_2}\) With \(a\) known, we can solve for \(b\): \(b= \frac{y_2}{y_1}\)

Step 4: Conclusion

Since we now have unique values for constants \(a\) and \(b\), we can say that the data points \((1, y_1), (2, y_2), (3, y_3)\) lie on an exponential curve of the form \(y = ab^x\).

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