Q. Find the value of ∫46x−83dx. Express your answer as a constant times ln2.Answer: □ln2
Recognize standard form: Recognize the integral as a standard form.The integral ∫x−83dx can be recognized as a standard form of the integral ∫u1du, where u=x−8.
Perform substitution: Perform a substitution.Let u=x−8, then du=dx. The integral becomes ∫u3du.
Integrate using logarithm: Integrate using the natural logarithm.The integral of u1 with respect to u is ln∣u∣. Therefore, the integral becomes 3ln∣u∣+C, where C is the constant of integration.
Substitute back for x: Substitute back for x.Since u=x−8, the integral becomes 3ln∣x−8∣+C.
Evaluate definite integral: Evaluate the definite integral from 4 to 6.We need to evaluate 3ln∣x−8∣ from x=4 to x=6. This gives us 3ln∣6−8∣−3ln∣4−8∣.
Simplify expression: Simplify the expression.Simplify the expression to get 3ln∣−2∣−3ln∣−4∣. Since the natural logarithm of a positive number is the same as the natural logarithm of its absolute value, this simplifies to 3ln(2)−3ln(4).
Combine logarithm terms: Use logarithm properties to combine terms.Using the property of logarithms that ln(a)−ln(b)=ln(ba), we get 3ln(42).
Simplify fraction inside logarithm: Simplify the fraction inside the logarithm.The fraction 42 simplifies to 21, so the expression becomes 3ln(21).
Use logarithm property: Use the property of logarithms ln(a−1)=−ln(a).The expression 3ln(21) is equivalent to 3(−ln(2)), which simplifies to −3ln(2).
Express as constant times ln(2): Express the answer as a constant times ln(2).The final answer is −3ln(2), which is the value of the definite integral from 4 to 6 of x−83dx.
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