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Find the average value of the function 
f(x)=(4)/(6-x) from 
x=7 to 
x=9. Write your answer as the logarithm of a single number in simplest form.
Answer: 
ln(◻)

Find the average value of the function f(x)=46x f(x)=\frac{4}{6-x} from x=7 x=7 to x=9 x=9 . Write your answer as the logarithm of a single number in simplest form.\newlineAnswer: ln() \ln (\square)

Full solution

Q. Find the average value of the function f(x)=46x f(x)=\frac{4}{6-x} from x=7 x=7 to x=9 x=9 . Write your answer as the logarithm of a single number in simplest form.\newlineAnswer: ln() \ln (\square)
  1. Set Up Integral: The average value of a continuous function f(x)f(x) on the interval [a,b][a, b] is given by the formula:\newlineAverage value = (1/(ba))abf(x)dx(1/(b-a)) \cdot \int_{a}^{b} f(x) \, dx\newlineHere, a=7a = 7, b=9b = 9, and f(x)=(4)/(6x)f(x) = (4)/(6-x).\newlineFirst, we need to set up the integral to find the average value.
  2. Calculate Integral: Now we calculate the integral of f(x)f(x) from x=7x=7 to x=9x=9. \newline7946xdx\int_{7}^{9} \frac{4}{6-x} \, dx\newlineTo integrate this function, we can use a substitution method. Let u=6xu = 6-x, then du=dxdu = -dx.
  3. Substitution Method: Substituting uu into the integral, we get:\newline7946xdx=134udu\int_{7}^{9} \frac{4}{6-x} dx = -\int_{-1}^{-3} \frac{4}{u} du\newlineNotice that the limits of integration have also changed according to the substitution u=6xu = 6-x. When x=7x = 7, u=1u = -1, and when x=9x = 9, u=3u = -3.
  4. Evaluate Integral: Now we integrate 4u\frac{4}{u} with respect to uu:4udu=4lnu\int \frac{4}{u} du = 4 \cdot \ln|u| Evaluating this from 1-1 to 3-3 gives us:4ln34ln14 \cdot \ln|-3| - 4 \cdot \ln|-1|
  5. Simplify Expression: Since ln1=ln(1)=0\ln|-1| = \ln(1) = 0, the expression simplifies to:\newline4×ln34×0=4×ln(3)4 \times \ln|-3| - 4 \times 0 = 4 \times \ln(3)
  6. Find Average Value: Now we need to divide this result by (ba)(b-a) to find the average value:\newlineAverage value = 1(97)×4×ln(3)=12×4×ln(3)=2×ln(3)\frac{1}{(9-7)} \times 4 \times \ln(3) = \frac{1}{2} \times 4 \times \ln(3) = 2 \times \ln(3)
  7. Final Result: The average value of the function f(x)f(x) from x=7x=7 to x=9x=9 is therefore 2ln(3)2 \cdot \ln(3). This is the logarithm of a single number, as required.

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