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The variables x and y satisfy the equation y = Ae^(-nx²), where A and n are constants. The graph of lny against x² is a straight line passing through the points (1.64; 1.76) and (3.69; 2.32). Find the values of A and the values of n correct to 2 decimal places.

Mathematics

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Answer

A=3.71,n=−0.27A = 3.71, n = -0.27

Step-by-step solution

5 steps

The given equation is y=Ae−nx2y = Ae^{-nx^2}.
We are told that the graph of ln⁡y\ln y against x2x^2 is a straight line.

  1. Transform the given equation into a linear form.

    Take the natural logarithm of both sides of the equation y=Ae−nx2y = Ae^{-nx^2}:

    ln⁡y=ln⁡(Ae−nx2)\ln y = \ln(Ae^{-nx^2})

    Using the logarithm properties ln⁡(ab)=ln⁡a+ln⁡b\ln(ab) = \ln a + \ln b and ln⁡(ek)=k\ln(e^k) = k:

    ln⁡y=ln⁡A+ln⁡(e−nx2)\ln y = \ln A + \ln(e^{-nx^2}) ln⁡y=ln⁡A−nx2\ln y = \ln A - nx^2

    Rearrange this equation to match the form of a straight line Y=mX+cY = mX + c:

    ln⁡y=(−n)x2+ln⁡A\ln y = (-n)x^2 + \ln A

    Here, Y=ln⁡yY = \ln y, X=x2X = x^2, the gradient m=−nm = -n, and the Y-intercept c=ln⁡Ac = \ln A.

  2. Calculate the gradient (mm) of the straight line.

    The straight line passes through the points (X1,Y1)=(1.64,1.76)(X_1, Y_1) = (1.64, 1.76) and (X2,Y2)=(3.69,2.32)(X_2, Y_2) = (3.69, 2.32).
    The gradient mm is given by:

    m=Y2−Y1X2−X1=2.32−1.763.69−1.64m = \frac{Y_2 - Y_1}{X_2 - X_1} = \frac{2.32 - 1.76}{3.69 - 1.64} m=0.562.05m = \frac{0.56}{2.05} m≈0.27317073m \approx 0.27317073
  3. Find the value of nn.

    From Step 1, we know that m=−nm = -n. Therefore:

    n=−m=−0.562.05n = -m = -\frac{0.56}{2.05} n≈−0.27317073n \approx -0.27317073

    Rounding to 2 decimal places:

    n≈−0.27n \approx -0.27
  4. Calculate the Y-intercept (cc).

    Using the equation Y=mX+cY = mX + c and the point (X1,Y1)=(1.64,1.76)(X_1, Y_1) = (1.64, 1.76):

    1.76=(0.562.05)(1.64)+c1.76 = \left(\frac{0.56}{2.05}\right)(1.64) + c c=1.76−0.56×1.642.05c = 1.76 - \frac{0.56 \times 1.64}{2.05} c=1.76−0.91842.05c = 1.76 - \frac{0.9184}{2.05} c=1.76×2.05−0.91842.05c = \frac{1.76 \times 2.05 - 0.9184}{2.05} c=3.608−0.91842.05c = \frac{3.608 - 0.9184}{2.05} c=2.68962.05≈1.3119999c = \frac{2.6896}{2.05} \approx 1.3119999
  5. Find the value of AA.

    From Step 1, we know that c=ln⁡Ac = \ln A. Therefore:

    A=ecA = e^c A=e2.68962.05A = e^{\frac{2.6896}{2.05}} A≈e1.3119999≈3.71320A \approx e^{1.3119999} \approx 3.71320

    Rounding to 2 decimal places:

    A≈3.71A \approx 3.71

    The values are:

    A=3.71,n=−0.27A = 3.71, n = -0.27
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