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Find the value of 
int_(3)^(8)(3dx)/(9-x). Express your answer as a constant times 
ln 6.
Answer: 
◻ln 6

Find the value of 383dx9x \int_{3}^{8} \frac{3 d x}{9-x} . Express your answer as a constant times ln6 \ln 6 .\newlineAnswer: ln6 \square \ln 6

Full solution

Q. Find the value of 383dx9x \int_{3}^{8} \frac{3 d x}{9-x} . Express your answer as a constant times ln6 \ln 6 .\newlineAnswer: ln6 \square \ln 6
  1. Recognize standard form: Recognize the integral as a standard form.\newlineThe integral 3dx9x\int \frac{3dx}{9-x} can be recognized as a form of the integral 1axdx\int \frac{1}{a-x}dx, which is a standard form whose antiderivative is lnax-\ln|a-x|.
  2. Substitution with u: Rewrite the integral with a substitution.\newlineLet u=9xu = 9-x, then du=dxdu = -dx. We need to adjust the integral to match this substitution, so we multiply by 1-1 inside and outside the integral to get 3duu-3\int \frac{du}{u}.
  3. Change limits of integration: Change the limits of integration.\newlineWhen x=3x = 3, u=93=6u = 9-3 = 6. When x=8x = 8, u=98=1u = 9-8 = 1. So the new limits of integration are from u=6u = 6 to u=1u = 1.
  4. Perform integration: Perform the integration.\newlineThe integral 3duu-3\int \frac{du}{u} from u=6u = 6 to u=1u = 1 is 3[lnu]61-3[\ln|u|]_6^1.
  5. Evaluate definite integral: Evaluate the definite integral.\newlinePlugging in the limits of integration, we get 3[ln1ln6]-3[\ln|1| - \ln|6|]. Since ln1=0\ln|1| = 0, this simplifies to 3[ln6]-3[-\ln|6|].
  6. Simplify expression: Simplify the expression.\newlineThe expression 3[ln6]-3[-\ln|6|] simplifies to 3ln63\ln|6|, which is 3ln63\ln 6 because the absolute value of a positive number is the number itself.