Q. Find the value of ∫27x−125dx. Express your answer as a constant times ln2.Answer: □ln2
Recognize standard form: Recognize the integral as a standard form.The integral ∫x−125dx can be recognized as a standard form of the integral ∫u1du, where u=x−12.
Perform substitution: Perform a substitution.Let u=x−12, then du=dx. The integral becomes ∫u5du.
Integrate using logarithm: Integrate using the natural logarithm.The integral of u1 with respect to u is ln∣u∣. Therefore, the integral becomes 5ln∣u∣+C, where C is the constant of integration.
Substitute back for u: Substitute back for u.Replace u with x−12 to get 5ln∣x−12∣+C.
Evaluate definite integral: Evaluate the definite integral from 2 to 7.We need to evaluate 5ln∣x−12∣ from x=2 to x=7. This gives us 5ln∣7−12∣−5ln∣2−12∣.
Simplify expression: Simplify the expression.Since 7−12=−5 and 2−12=−10, and the absolute value of a negative number is positive, we have 5ln(5)−5ln(10).
Use logarithm properties: Use the properties of logarithms.We can use the property ln(a)−ln(b)=ln(ba) to combine the logarithms: 5ln(105).
Simplify fraction in logarithm: Simplify the fraction inside the logarithm.The fraction 105 simplifies to 21, so the expression becomes 5ln(21).
Bring constant outside logarithm: Use the property of logarithms to bring the constant outside the logarithm.Since ln(ab)=bln(a), we can write 5ln(21) as −5ln(2) because ln(21)=ln(2−1)=−ln(2).
Express final answer: Express the final answer.The value of the definite integral from 2 to 7 of x−125dx is −5ln(2).
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