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Evaluate 
int_(1)^(8)(x-8)/(x-9)dx. Write your answer in simplest form with all logs condensed into a single logarithm (if necessary).

Evaluate 18x8x9dx \int_{1}^{8} \frac{x-8}{x-9} d x . Write your answer in simplest form with all logs condensed into a single logarithm (if necessary).

Full solution

Q. Evaluate 18x8x9dx \int_{1}^{8} \frac{x-8}{x-9} d x . Write your answer in simplest form with all logs condensed into a single logarithm (if necessary).
  1. Evaluate Integral: We need to evaluate the integral of the function (x8)/(x9)(x-8)/(x-9) from 11 to 88. To do this, we will first perform a partial fraction decomposition if possible. However, in this case, the numerator is of lower degree than the denominator, and the fraction is already simplified, so we can proceed to integrate directly.
  2. Rewrite Integral: Let's rewrite the integral by splitting the fraction into two parts:\newline18x8x9dx=18(1+1x9)dx\int_{1}^{8}\frac{x-8}{x-9}\,dx = \int_{1}^{8}(1 + \frac{-1}{x-9})\,dx\newlineThis is done by dividing x9x-9 into x8x-8, which gives us 11 with a remainder of 1-1.
  3. Integrate Separately: Now we can integrate each part separately:\newline18(1+(1)/(x9))dx=18dx+18(1/(x9))dx\int_{1}^{8}(1 + (-1)/(x-9))\,dx = \int_{1}^{8}\,dx + \int_{1}^{8}(-1/(x-9))\,dx\newlineThe first integral is straightforward, and the second integral is a standard logarithmic integral.
  4. Evaluate First Integral: Evaluating the first integral gives us: 18dx=x18=81=7\int_{1}^{8}\mathrm{d}x = x \bigg|_{1}^{8} = 8 - 1 = 7
  5. Evaluate Second Integral: Evaluating the second integral gives us:\newline18(1x9)dx=lnx918\int_{1}^{8}\left(-\frac{1}{x-9}\right)dx = -\ln|x-9| \bigg|_{1}^{8}\newlineWe will evaluate this at the bounds 11 and 88.
  6. Evaluate Logarithmic Part: Plugging in the bounds for the logarithmic part, we get:\newlineln89+ln19=ln1+ln8=ln(1)+ln(8)-\ln|8-9| + \ln|1-9| = -\ln|-1| + \ln|-8| = -\ln(1) + \ln(8)\newlineSince the natural logarithm of 11 is 00, this simplifies to:\newlineln(1)+ln(8)=ln(8)-\ln(1) + \ln(8) = \ln(8)
  7. Combine Results: Combining the results from the two integrals, we get:\newline7ln(1)+ln(8)=7+ln(8)7 - \ln(1) + \ln(8) = 7 + \ln(8)\newlineThis is the final answer, and it is already in the simplest form with a single logarithm.

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